You may have read my other post about changing glow plugs without intake removal. There was a MB diesel specialist who I cannot find now that states the "impossible looking to access" glowplugs on the 300 and 350 series can be changed without intake removal. I would love to see how. Just getting the wiring harness off without removing the intake looks tricky as hell. I don't see how you would ever get to the couple plugs most hidden by other stuff even if you managed to get the harness off. I've also heard that the glow plugs can get impossibly stuck after being in for a long time. Breakage trying to get super old plugs removed can happen as well. Is there a good way to avoid damaging old "tough to remove" plugs? Are there special tools to pull this off?BTW- which of the three glowplugs offered is right for 1990 350SDL? they list three different plugs that fit this one. Which multi meter setting do you use to check the plugs, there's so many

The glow plugs on the 603's are not known to give problems on removal. The newer 606 suffers from this issue.

The special tools are usually a good set of extensions..........preferably wobble.

You check the plugs on the lowest possible setting of the meter. You're looking for about 1 ohm. However, a functional glow plug on the 603 is no assurance of a white hot plug. My '86 has functioning plugs..........but, I'd hazard a guess that they are just barely functioning based upon the start.