OK, I've finally become a believer in synthetic oil and have been running it in my GT for a year and am happy. I'm now going to expand it's use and put it in a LT which is a '80's Briggs 280700 and my push mower which is a 92500, don't remember the vintage, but it's the one which I discovered had the wind up starter as an option, so it's an oldie.
There's a few other 4 cycles around that I'll also be converting to synthetic oil.
My question is, should I use the traditional 30 weight or a 5 or 10-30? The GT is the only one I run in winter to plow snow and it's happy with 5-30.