Look in the owner's manual and see if you find an illustration of the affected wheel and bracket, then either post that datum here or send it to me e-mail.
On page 10 of the manual you sent me, I see a deck wheel and bracket, is this the "free and astray" wheel assembly?
And you could post a pic or send a pic to me, either way.
My first option to consider would be to have the wheel bracket welded back in place with a reinforcing plate or "gusset plate", or both plates........to make a dependable repair. With you not choosing this as a first line action, I will guess you did not buy any stock in welding products :^)
Show me the picture and I will advise.

If you look back a couple of feet you'll find a 5/16"x1 1/2 carriage bolt with a locknut on it, probably sheered. If not, that's what you'll need to re-attach that guage wheel assembly. You can usually find plated hardware in bulk bins (Ace) so you won't need to sell any of your Apple stock.

mownie I did not realize it was you to whom I sent the manual

The wheel is in the picture at the top of the page 10 in the LT-155 manual. It can also be seen on page 24, page 32 and a couple of other pages.

When I put the tractor away I did a quick check of the thickness of the deck, it seemed thin, but the fitting was welded to the deck originally and it has held up for ten years. The break is at the base of the fitting at the edge of the original weld.

After I finished up and came in and posted my request.

I will take pictures tomorrow.

I am more equipped for wood working than metal so would have to find someone to weld it.

I have also contacted the Reynolds Farm Equipment, the local JD dealer. They sell and service everything from toy JD's to the large farm tractors that turn by pivoting in the center. While primarily servicing Farm equipment, they very competitive on the small tractors as it is fill-in work and provides work in the winter when farm service is slow.

Images below describe how "I" would implement a repair using a reinforcement base plate of 1/8" thick steel welded to the deck. The base plate would be sized as dictated by the curved shape of the deck shell. Some shaping of the base plate would be done to assure a close fit.
I would drill 3/8" or 1/2" holes in the base plate as shown in first image to permit plug welding, which adds to the distribution of the loading better than simply welding along the perimeter of the base plate. Also in the first image notice that 1/8" needs to be trimmed frnd of the wheel bracket (where the OEM welds were) to retain the OEM dimensions of wheel placement.
Second image shows how I would add a "corner gusset" to stop the side flexing of the wheel bracket (which is what broke the OEM welds).
Print the images and carry them to a welding shop and they should have no problem in putting it to use.

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Okay so you knocked the entire casting off, no big deal. I just fixed one of these on a GT5000 deck for a fellow, 48".
After quizzing him, I learned that he was mowing the same pattern each time, and kept whacking the same stump.
I cleaned everything up, and mig welded it in place with a good degree of penetration, something Deere has never been able to do, painting the area with Rust Oleum, $35.00. You won't need to sell any USAGX either, the bulk of my SEP IRA.

I am the person that posted the original request 9 years ago. The wheel that broke was the 3" wheels on the front of the mower deck. The wheel broke out of the deck. In looking at it I realized the the piece that broke out fit neatly in the hole in the deck.

I could have tried to place a plate behind it as suggested, but after evaluating the options and talking to the John Deere Dealer, I decided to take it to him. They worked on everything from lawn tractors to to the huge farm Combines that you meet and take both lanes of a two lane road, so I assumed they could handle my mower deck. I took it in and they welded it back into the deck, cleaned it up and painted it. They did the work for wha I though was a reasonable price even for those tight times.

About two years later, the wheel on the other side of the deck did the same thing. We had moved out of state, so I took it to the local John Deere Dealer that did similar work. They charged me $40 dollars to weld that one back on, clean and paint the deck.

That Was in 2013, and I am still using the tractor, and have not lost any wheels since.

I could have done what was suggested and bolt a plate to the deck and attach the wheel, but on analysis I would have had to buy the plate, the bolts, and spend a couple of hours doing the work. With the flexing of the deck I doubt if the plate repair was as good as having it welded professionally. It did not seem cost effective when considering the dealer only charge $40.

Unless the break left the deck in two pieces I think I would consider having some one weld it back together. I would suspect that any shop that worked on large equipment could have done an equally good job.

Whatever you do, one comment that was given to me by dealer. The guide wheels are to prevent scalping. So they should be adjusted so they spend most of the time while you are mowing about an inch or two above the ground. Lower and with constant ground contact, they wear quicker and and are more likely to get a hit that will break them.

Contact me privately through the board, and we can exchange email messages so I can send you pictures.

I have no idea how to email on here. But yes, it was the 3" little wheel that came off. It left the rectangular hole and everything! I reached out to my neighborhood and I have a welder around the block! He is going to take it to work on Wednesday for me. I will have him sure up the other wheel too, just in case!