I have a 42" Fastrak Super Duty. At about 70 hours, I began to notice the left rear tire "slipping" when I engaged the steering handles....mower would veer left. Since the initial service for the tranaxles is at 75 hours, I went ahead and serviced the them with new oil, filters, etc. I followed the purging procedures to a "T" but I'm still having the same problem. Funny thing is, after the mower has been used at sits up overnight, I have to add more oil to the expansion tank. I've checked everthing thoroughly and cannot find the slightest leak from the filters, drain plug, or hoses. Upon starting the mower for the first time each use and running it for a few minutes, I still see air bubbles exiting the line into the expansion tank.....always from the same side. Also, after running the mower for about 10-15 minutes and it heats up really well, the "slipping" seems to improve. Any thoughts/input?