My 850-T has been leaking from the rocker covers ever since I bought it and even after the engine rebuild with new gaskets. I tried tightening up the allen head screws and tried applying aviation form-a-gasket #3 (it works, but makes it interesting to get the covers off). I put the question to Mick who showed me a neat method of getting a great result.
Arm yourself with corse valve grinding paste, 3-in-1 oil and a sheet of glass. Put some valve grinding paste down on the glass and mix it with a bit of the 3-in-1. Rotate the rocker cover in the mix until the surface contact area is flat with a rough finish (it'll look a bit like cast when you're finished). After a few minutes of doing this, have a look to see what the valve grinding paste is doing. Its easy enough to spot the highs and lows in the metal. As you're going you'll notice the mix becomes less effective, so a bit more vavle grinding paste and 3-in-1 may be needed. No need to put your whole body weight on the thing while you're rotating it, just the weight of your arm will do fine. It could take you a while depending on how bad the undulations are, so grab a beer and turn up the music.
When you're finished, wash the rocker covers thorougly with petrol to remove the vavle grinding paste. Put new rocker cover gaskets on and thread each screw down until it just starts to bite. A quater turn more is all that's needed and hopefully, say good bye to the leaky rocker covers. You could probably use the same method to fix a weaping sump where the gasket is failing to seal properly.
