OK, have a knocking on my recent purchase 300e. Have read most of the engine knock threads and acted on them, but am still a little iffey on what might be the culprit.. hope somebody can help me out with some insight/experience.
The issue:
Engine has a knock, more present on idle, and on release from throttle. Absolutely is mechanical and within the block.
Noise does not start with start up of motor- there's about a 2-4 second delay from start-up to when it's present. I'm thinking a bearing, rod, or wrist pin would be there as soon as that cylinder spins.
Broomstick to ear test confirms its on cyl 6, though manifold makes it hard to guess where. Sound seems to be present through height of cylinder.
Exhaust has a noticeable mild hiccup every now and then. Very subtle.
All cyclinders were around 90psi on first crank, 120psi peak for compression, middle cylinders less so (70psi on first crank).
Knock is present,even when all other plug wires are pulled individually, greatly diminishes when numbers 6 plug wire is pulled.
No lack of power. am running 93 octane, and have run fuel injector cleaner and a batch of 104+ in it to clean out gunk. Have run a few tankfuls of fresh gas through it.
Pulled valve cover, and a quick glance didn't show any major issues.
At some point, PO suffered broken antifreeze holding tank, and looks to have baked head (from underneath, edges of head look amazingly clean in comparison to rest of engine)
I've driven this 30 miles at a crack about every day for the last week. Does not seem to be getting worse.

so, I've got three views on this so far:
1) Oil galley/etc. is blocked, run car w/ some marvel mystery fluid for a bit to clean out sludge and replace oil.
2) Broken valve spring. Causing hiccup in idle, and noise on head.
3) some combination of shaving head beyond clearance, valve striking cyclinder.
4) Valve adjustment, etc.
5) wrist pin or bearing.

Any thoughts? Anyone run into a similar situation? i'm also thinking about running some synthetic, and would welcome anyones views on which to run.
thanks.. !