Remove the seal on end-shaft block/cap and ensure the bore in this block/cap, bore in the new Crankshaft Seal, the contact surface of crankshaft is free from scratches, nicks which may damage the new seal lip and lead to oil leakage; if the crankshaft is damaged, then a suitable new crankshaft or different one has to be procured. As a matter of fact, engine oil or, better still, multi-purpose grease ought to be spread lightly on the outer lip of the new Crankshaft Seal besides spreading moly-base grease or engine assembly lube on the seal lip. Nice it the seal lip over the end of the crankshaft and gently drive it in using hammer and punch and make sure you have covered the bore through the circumference of the Crankshaft Seal making sure it is squarely seated.