One of the problems you can experience with Triumph engines are big end seizure. The result can be a totaly wrecked engine......
It`s importent to clean the oil slugde filter in the crank. On older three piece cranks, take them apart and clean inside.
On pre unit Triumphs I always get the register cover machined to accept a oil seal.
The original bush will let the oil go past:
Ready machined and assembled. A segerring keeps the oil seal in place: