400E/119 Valve Seal Replacement
 

My car needs valves seals and I was thinking of doing it myself. While the valve covers are off, I was thinking about replacing the upper chain guides and tensioner. I've never had a timing chain off an overhead cam engine and, with 32 valves, I'm not sure I want to risk not getting things back together correctly. Can the seals, guides and tensioner be replaced without actually removing the timing chain? Also, how hard is it to replace the valve seals? Is there a risk of dropping a valve into the cylinder on a job like this? Any special tools required? Thanks.

I noticed from the manual that there is a special tool to remove the guide rail (tool #119 589 01 63 00) (first diagram) and a cam lock tool to ensure that the exhaust cam doesn't jump when the timing chain is released during the tensioner removal (tool # 111 589 03 15 00) (second diagram). Does anyone know if you can get away with a substitute?

It looks like the cam has to come off to do the seals. Maybe I'll have the shop do the seals and stick with only the rails and tensioner. Any input would be appreciated.