They can be repaired if you can fu=ind a shop that repairs hydros by machining the kidney plate & valve chest then shimming them to the right spec .
Some old time tractor shops as in farm tractor shops do this because a lot of old heavy ( 100hp ) draught tractors had a hydro drive for going really really slowly
The Oliver we had here was 1 mph in first to 5 mph in top with a hydro to drop that even slower but more important have no mechanical connection between the engine & the wheels
And oddly enough a tractor the neighbour has uses a hydro for road gears , a whooping 10 mph, which id frighteningly fast on top of 48" wheels with 15 ton under you .