If you can find a working transmission for a GR series for $1500, I'll buy a bunch of them and resell them!!
The last one I put in was over $4000 installed at the dealer. Mind you there was other labor involved for other items he wanted addressed but IIRC the trans itself was around $3300.
They are expensive to fix. They are weird. You gotta know them. IOW if you ain't had one apart, you're in for a real treat. The pto clutches were poor. The transmission itself was poor. The actual HST part of it never dies or at least I've never heard of it. It's always the PTO clutch, the axle bushings, the glide-steer clutches , the differential in that order of most to least common. When the axle bushings go south, the axles leak. "Most" of the time it takes out the housing too, and it's usually on the older units more than the newer ones. Then the housings. There is a channel that runs all through them, that is used to vent the transmission assembly, you have to be mindful of it, and where it's at, and what it does--if not, it'll puke oil out of it, knock the seals out, etc. Just a stupid design all around--and quite commonly is the #1 reason that GR series mowers get retired.
I absolutely love most of the rest of the mower other than it's slow, it's sure footed, cuts wonderful, sips fuel. But the transmission and it's expense to repair/replace are the ONLY reason I wouldn't own one; and I speak for many who feel the same. It is, a big step backwards from the G1800/G1900. If the G series had power steering, they would have been one of the most popular mowers ever. But I think the marketing dept saw that it was fast and since the ZT's were starting to gain popularity, the marketing team saw that the G1800/G1900 was stealing the show from the ZT's, so they replaced it. Might have been more to it, possibly costs rising, etc. I never know all that important stuff. I had a G1900 for a long time and I'd still have it if a man didn't offer me what he did for it. Money talks. But I had a Kommander, and like it, so I said yeah man, it's yours.