Ok... I was hesitant to post this but eventually figured what the heck someone may have ran into the same thing. Bear with me.... :-)
I've had my X500 for 4 years. I changed the transaxle fluid at 50 hrs. and never had to add a drop since. When cold the level always stays right at the full mark on the reservoir tank.
So two weeks ago I hit 200 hrs and it's time to change the transaxle fluid again. To minimize confusion on how much to add back in I measured the oil that I drained out and then added that exact amount of Lo-Vis Hy-Gard back in. As expected it brought the level right back to the full mark. I ran the tractor, checked for leaks, good to go.
I've put about 4 hours on the tractor since the oil change including mowing the grass twice. Oil level has stayed right on the full mark.
Yesterday while in the garage I happened to look at the reservoir tank and the oil level was down to half way between full and add. I looked on the floor - no leaks. I crawled underneath and felt around all the bolts and drain plugs - no leaks. So I figured maybe it was due to the extreme heat in the garage so I waited until early this morning and checked it again. This time the reservoir tank was empty!! Huh? Again, no oil drops on the floor and no leaks to be found anywhere around the transaxle housing. Where did the fluid go? And why now after 4 years of the fluid level not changing?
So I went ahead and added some fluid to bring the level back to the full mark. I didn't measure it but I doubt it took more than 3-4 ounces of fluid to take the tank from empty to full, which really surprised me.
So I am still very confused and at this point will just continue to monitor the fluid level. I know common sense seems to say that there must be a leak but with no fluid on the floor and no fluid to be found anywhere on the transaxle or reservoir tank I don't see how.