If it was mine, I'd sell it while it is still going great, and buy a new one for future trouble free service. You are "whipping a dying horse" as the saying goes.
While it gives you bragging rights for the length of trouble free usage, the fact that nothing is available right now for your machine, makes me wonder what you will do when it finally gives up the ghost!
That said---There are a few lawn equipment grave yards scattered around the Country. But, your chances of finding a good transmission are very slim. There is no way i know of, to check a tranny without installing it first. Then you must try it out. And, if it doesn't work, you are stuck with it!
I accept old lawn equipment donations, and use them if they work well. If the engine is good and the tranny is bad--the engine becomes a sale item. Or, if i have a tractor with a bad tranny, the engine and other parts are stocked for future use or sale. Used tranny's? Nothing. Especially the so-called automatics, or what ever fancy name they call them.

It is a valid pursuit to try and maintain older equipment if that is what one wishes to do, but......you may be forced to deal with the "used parts market" for components.
If you intend to supply the labor for this (aka DIY) then you should not be too worried about the transaxle R&R until you simply can't find any used ones any longer.
If, however, you are intending to pay someone else to perform the work, rusty's opinion gains some strength.
But if you are EXTREMELY resourceful and have the experience, tools, determination and cash, you could conceivably retrofit a different transaxle to the chassis.
You just gotta decide what's right for you.

You might be resourceful and do some preventive maintenance.
Here's a link to a diagram with a parts list.
Order new grease and install?

http://www.m-and-d.com/pdfs/foote/4450-3.pdf

http://www.m-and-d.com/FT-1866.html

Thanks everyone for your thoughts. After the engine quit I did look around for a new rider mower. Due to a lack of garage space a riding tractor was not an option. Anyway, the cheapest riders I found[there's not many out there]were a craftsman and a MTD sold at Lowes. They sold for about $1000.00. Unlike my Murray mower which is all metal the frames on the new mowers were made of cheap plastic. On top of that it would cost me an additional $300 or so for new accessories. My Murray grass catcher still works fine. It cost me roughly $500 to install the new engine. So if I get another year or two out of it great!

I agree with bill, not that hard to remove and disassemble and all you would have in it is your time and tube of grease. Clean up, regrease, and reseal is probably all it needs.. I done my 20 year old and it looked like new on the inside other that grease was old.

Bill and rcmoser, I kind of agree with your idea of preventive maintenance. I have always been meticulous about changing oil, air filter, ect according the maintenance schedule in the manual. However, the manual does not mention any scheduled maintenance for the transaxle. Even though it does not mention it, it seems like good idea after 16yrs of operation. Removing the axle seems straight forward. I found a drawing and P/L on the internet for my transaxle. The drawing shows an exploded view of the transaxle and its parts.

From the drawing, it shows about 14 screws holding the cover on. My concern is having a part fall out after removing the cover and not knowing where it came from. As I mentioned, the drawing is an exploded view and does not show how all the pieces fit together inside the housing.

Do either of you know if there exists some kind of manual similar to a car shop manual that would show in detail the assembly and disassembly of this transaxle? Also, once it is opened I could check for worn gears. Found a few websites that sell used parts for this transaxle. If worn I would like to replace them.

Again, thank you for your inputs.

I am of the school of thought "if it ain't broke, don't fix it". Plus, if it has a grease nipple, grease it, but if it cannot be greased, or the oil in it changed without taking it apart, then leave it alone, especially if it is not giving you trouble; to me that is just asking for trouble.

GOggle and Utube it show excellent video on it.... Not that hard just got to know about the slector ball and spring. video show it in detail...... As I said mine was 20 years old and wasn;t that bad. but the grease was seperated and old made it hard to shift and not roll easy. I think you could go ac/dc either way leave it alone or regrease and clean up the rear area... up to you.

I have seen several Utube videos on disassembling riding mower transaxles and it looks relatively easy. As long as the Spicer gear parts are still available I will leave it alone for now until the first signs of trouble. The transaxle is 16yrs old. I usually mow once a week, but in the summer when it gets real hot I usually mow every other week. I think there's still several years of life left in this transaxle.

Thanks again for your thoughts!

Has anyone out there seen the Youtube transaxle repair video called "How to repair a transaxle, sorry no mower mudding in this one.. . Following a minor repair, the mechanic cleans all the grease off the gears and the inside of the transaxle case. Instead of applying new grease, he uses a mixture of gear oil and Lucas Oil Stabilizer. The stabilizer causes the gear oil to adhere to all the moving parts. This lubrication scheme seems so much better than using grease.

After 16 years of service on my lawn mower transaxle, I want to open it up, inspect it. and if necessary, replace any worn parts. Prior to closing it up, I want to add a lubricant. Dana, the transaxle manufacturer, recommends a grease P/N FT-4000.

I like the idea of using the gear oil mixture instead of the grease, Has anyone else out there tried using the gear oil mixture? If so, how did it turn out?