Any Sanshin hub is likely to be 30-40 years old. Plenty of time to have have several bearing cleanings, perhaps new balls and cones (which may or may not match the old ones.. Likewise washers and locknuts. Quite possible that on assemble a little too much axle struck out one side or both. As several posters have pointed out, if this is the case, you will NEVER get you quick release tight enough to keep the axle from slipping. Add washers between the cone and the locknut. If you use thin ones on both sides, the wheel dish and brake pad settings won't change.

When you finish, the axle should not reach the outside of the dropout when in contact on the inside with the locknut. Now, all your QR clamping force is on the dropout, not the axle. (Actually the axle extension past the locknut isn't even needed once the QR is tight. It's function is primarily as a guide into the dropout.)

Another thought - it is possible the axle was replaced with a longer one or washers and spacers removed to use a narrower dropout spacing in a different bike. Again, a lot can happen in 40 years

Ben