Been working on this for awhile, misfire codes on all cylinders but no other codes. Checked and fixed vacuum leaks, exhaust leaks, replaced MAF and O2 sensors, cleaned and checked all other engine timing sensors, oil and fuel pressure good. Now looking at chain stretch, values are -8 and -10 for blocks in VCDS 208 and 209, should be at least -8, also "detected 1 exhaust phase flank" is 135 should be 118 to 134 degrees. Thinking it is just on the edge and would like to catch it early. AXK engine with 240k miles.

In few days doing "exploratory surgery", taking off intake manifold, valve cover and upper timing chain cover. Hoping it is just a busted guide, but not sure what can be replaced with just the upper cover off. I assume the upper guide can be replaced, but can the upper left or right chain guides be replaced or even the upper chain? I realize the intermediate sprocket and lower guide rails are all covered and inaccessible, but not sure about the upper ones and would like to have new parts on hand.

Also have the classic timing chain cover oil leak and see that when you put the cover back on there is no gasket, just sealant. What sealant should I use?
Thanks,
   Steve