Don't worry about a Walker engines. They are the weakest part of that machine. Because they are so enclosed and low to the ground they run hot and don't last but 1200 to 1500 hrs. I have a 1993 that i just retired because I retired from mowing. It went through more motors than I can remember over the years.
I have nearly 3000 hours on my walker, original engine, hydros, everything. I hope to get 1500 more, and I think I will. There were just some bad Kohler 25s for several years (mine is a 20), so find a mechanic that KNOWS THE BAD KOHLER years, if has NOthing to do with Walker.