68 E-Type 2+2

A while ago I posted a speedometer problem. Since then I had it repaired & asked what caused the problem.I was told that the seal was leaking gear oil from the cable drive & wicking up to the speedometer causing it to get gummed-up. I purchased a new seal but can't get the old one out. Removing the right-angle drive would appear to give you access but the housing has an integral cap which prevents you from pulling the old seal out. The output housing is threaded all the way from the end into the tailshaft. I'm not sure if I should lock 2 nuts together on the housihg & try to back it out of the tailshaft to give me access to the seal. Any ideas?