I have a 67 Silver Shadow. On cold starts the exhaust spits out a very foul white smoky exhaust, then it settles down after the car warms up. I am told that the problem is leaking valve seals. Have you or anyone else tried to replace the valve seals on your own (without removing the head). There are a lot of videos online that demonstrate the process. I am reaching out to RR owners to get some feedback.