I changed mine a while back. Maybe this post will be of help to you.
400E Upper Chain Guides
Regarding the timing chain stretch, I was never able to get a definitive answer on how to check it. The job in the shop manual (attached) has a procedure for "[c]hecking, adjusting basic setting of camshafts," and it has you pin all 4 camshaft sprockets with the 6.5 mm pins at the camshaft bearing caps, after turning the engine so the vibration damper is at 45 degrees BTDC. It says that "it must be possible to pin the camshafts with the pins," but it does not say what it means if you cannot do this. Then it goes on to tell you to "fit on" the timing chain (maybe I missed it, but I can't find where it has you take it off).
I was wondering if you could check for stretch by turning the engine until the pins
did align, then check the damper to see how far off from 45 degrees it is.
Any thoughts on this?