the bolts are a weird style bolt-tapered on the ends, sort of like self tapping. They probably are, in other words the cast trans case most likely did not have threads after the casting process and they just run the bolts in, which would explain why they're so tight and most of the time seized when I go into them. When they break, they are harder than hammered heck to get them drilled out. NO seriously, they are HARD. They laugh at a HSS drill bit (usually) as if you were trying to drill into a piece of glass, or tool steel.
I honestly wouldn't bother going into it. Pain in the neck.
take it out of the mower frame and turn it upside down over a bucket with the fill tube removed. Let it drain for a day or 3. Make sure the bleeder screw is out. The WSM shows it. Just refill it, as I recall about 3 quarts. Synthetic is a waste, it makes no difference in an HST. 20w50 cheap stuff is fine. Only time I've noted any difference was with some dual hst equipped zero turn mowers that people like to use as demolition derby, jam the levers as hard as they can forward and backward at breakneck speeds, skidding the tires, tearing up the lawn but hey--they didn't buy it to go slow. On those types, some have noted slightly less noise but that is all. But if it makes you feel better, by all means synthetic.
the other reason I say leave the pan on is that the filter--that filter is a pain in the backside. Most people just grab it and pull, and out comes the filter seat. Well there is a spring & ball under it, if it falls out (and it almost always does), you don't know where it goes, and hydrogear doesn't tell you and neither does the WSM since the WSM more or less paraphrases what hydrogear told them. So you just have to figure it out, which is kinda fun. Reassemble it and find out that it don't move. Pull it back out, drain it, remove pan, put it in a different hole, try again.
