The original timing cover had a felt seal (made of wool?) that "restricted" oil flow. Later BMC vehicles had a rubber seal. I decided to upgrade mine to hopefully slow the oil leaks. You can see the differences in the shot below. The cover can be purchased new for $300 AUD, or a second hand one for under $100, I took the later option!
I fitted the cover and loosely did up the bolts. Then used a series of ratchet extenders and a large socket to tap the crankshaft pulley into place. This (in theory) should help centre the seal and pulley join. I then did up the bolts. Used a paper gasket! Paper, wool, leather - amazing materials they had to use in the old days to prevent oil leaking.