I agree that the likely culprit is worn valve guides, which is no big deal if the smoke isn't obnoxious and oil consumption is within reasonable limits. However, those B18-style seals on top of the retainers do just about nothing to control smoke on deceleration -- if you leave them off entirely, you'll get a brief puff of smoke on start-up, but no further smoke as long as the guides are not worn beyond spec.