I like the last idea
The most noticeable instance of leakage is when loading empty trailers back onto trucks, as the trailer is off balance and the grapple rotate is on a vertical plane.
I havn't had the chance to try changing the checks to a Hot oil shuttle. I'm surprised they use the open loop version of the motor as the lube oil for the bearings is taken from the high pressure side, resulting in oil loss like you say, and extra heat buildup as there is a large pressure drop from the high side of the motor to the drain. My opinion is that taking oil from the return side, or low pressure side to lube the bearings would be a much better idea. Less drift, less heat build up, better efficiency. Seems to be a win win. The major concern is making sure there is enough back pressure so that the lube oil supply is not lost, resulting in bearing failure.
Weldco But'n top grapple use two of these motors in parrallel to rotate the graple, I don't know if you could get a rotator like Rotobec Indexator in a displacement large enough. It would require a lot of modification though, the HOS valve swap should be pretty easy to do.
If I get an opportunity to try it out, I will be sure to post the results.