MBs Only Now

Once again, thanks for your earlier reply. I pulled out the suppressor/insulator cap and found it to be in excellent condition, although there was a tiny bit of oil between it and the block (the oil leak will be the next good time in which to engage). I cleaned the back of the cap and the area of the block before reassembly... No hesitation now for three days! Go figure that the thin film of oil was causing all those headaches!

MBs Only Now

Hi Rod. Had you not mentioned this part, I would not have pulled it to discover a thin layer of oil between it and the block. It was the cause of my headaches! Now a leak to fix somewhere.

I was wondering where you may have been putting your code reader? My Canadian market 1992 300SL only has a 9 pin diagnostic port (like a couple of others I've encountered that have earlier r129 300SLs purchased here). I have a code reader that tells me in the included PDF that I'm SOL without something else. Cheers.

Auzivision

Mine needed replaced when I bought it with around 80K on the clock. I drove it/fought it for 5K miles and replaced about everything but this disk! This fix worked for me and I did it myself.
Every shop visit, it temperately appeared that my mechanic 'fixed' it only for it to return (it being the intermittent mis-fire). Change the Plugs, worked for a while, changed the wires, worked for a while, changed the computer, worked for a while, changed out the cap, Rotor, and coil, worked for a while. Replace this shield and the mis-fire is totally gone. Cold days, Rain days, long rests, still no mis. Fingures crossed.
Now for the interesting part. Other than being somewhat faded, the shield looked good. No cracks no chips. My theory is the seal gets compromised and lets in moisture. Every-time the mechanic "checked" and "fixed" it he would open the cap to inspect and let the moister escape. The longer it sat, the more it would leak in moisture. After long drives, moisture would evaporate and the mis goes away. It often was worse when cold because of condensation. That fits my symptoms to a Tee.

My other theory is dielectric properties of the material breaks down with age, but that wouldn’t explain the intermittent behavior. Either way, anyone having troubles with an unusual mis fire with a 300SL should probably start with this part. It's almost the cheapest of all things ignition related.

Oh yeah, and kudos to this thread… This is where I got the idea to try this fix.
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Bill300sl

I was having the same issue a couple of years ago and discovered the "O" ring hadn't seated correctly; replace it and no problems until last fall in the rainy season here in northern CA, it went from stalling when it came up to temp (80 C) and finally got to the point it would not even start. After reading this post, I ordered the dust cover and when I went to replace it, found I had ordered the wrong part, so I greased the "O" ring and put everything back together; car started and runs smooth again and have driven for 3 days with no issues. Dealer was the only place I could locate the dust cover part ($135) and I'm going back to get a new "O" ring.

Will put this on my calendar to replace the "O" ring yearly...