@Mario
looking at the TMs i have, the driven side (driver side, drum lock and free spool/engage handle) or non powered side as you called it, TM 9-2320-260-34P-2 FIG 380 item # 7 P/N 10875107-7 NSN 5330-01-119-5801 and in the tm link you provided TM 9-2320-272-34P-2 FIG 387 item # 34 large seal, seems to be difficult to source, even with the FSN web link you provided. Big Mikes show to be sold out, but he has the small seal fig 380 item # 41 and fig 387, item # 31 small seal, which cross references to the FSN link you posted. Were you ever able to locate the driven side seal? Did you by chance take measurements of the seal?