If it's a three bolt and never been rebuilt and been bored and fitted with needle rollers there's the start of the issue. The bronze bushes wear and the shaft moves and flexes the seal plus the hardening wears on the shaft at both the bush area and seal point. Shaft needs to be ground and re-hard-chromed then have the box bored out to fit bearings. Really the only solution, or buy a new 4bolt box whichj should have bearings from new, bolts straight in.

