The “common” two sizes for the guide OD when using aftermarket seals are .500 or .530.

If your guide tops are not either of those sizes I think you’ll have a hard time finding seals.

The “tool” can be used in a hand drill.

You’ll need the appropriate pilot as well.

5/16 and 8mm are only a few thou apart, so 5/16 seals will work fine.