My idle was getting rough so I decided to service the injectors. Last time I was in there, I noticed my rubber blocks and gaskets were in bad shape. I sourced the gaskets from Worle Fahrzeugtechnik for about $60 and the rubber blocks from Niemoeller for $300. I removed the head covers and used a 17mm flare nut socket to loosen the injector hoses. I used a magnetic 10mm to remove the nuts on the retainer block and a magnetic reach tool to grab the spring washers.
Mercedes Source sells a fuel injector metal line replacement for $30, and it makes removing injectors go quickly. Spin a couple of threads onto the injector then yank straight up from the intake. The bakelite retainer will come loose and then you can twist away at the injector. I found that they came out and went in best starting parallel with the ground and then working them vertical until they were seated.
The old gaskets were brittle and fell apart. There was evidence that air was getting past. I placed some blue towels on the head and then scraped away with a small wire brush. Then I got the idea to use a 20 gauge cotton swab from my shotgun cleaning kit to clean the injector hole. Works great.
I used Mercedes Source for the injector tester, and I had four very dirty injectors with one that was spraying with low pressure. I used a mixture of diesel purge with some ATF, and ran it through each for about 5 mins pumping around 400psi. Seven were popping around 215psi but one started spraying at 125psi. I eventually got it clean enough to pop at 205 but it would jump back down to 140psi. No good. I had a NOS injector ($200 eBay) and decided to run it on the tester. Good thing because it was tight. It didn't start releasing until 320psi and had a bad pattern but eventually settled at 240psi. That's all within spec.
I put everything back with some permatex aviation gasket sealer on the paper gasket and around the base of the injectors where they snug into the rubber blocks. Starting the 10mm nuts would have been impossible without the magnetic socket. I used some digital calipers to measure 33mm from the top of the bakelite to the machined surface on the intake. The new rubber blocks were painted black and all of the paint flaked off into the head when they started deforming from tightening them down. More cleaning.
It took a few cranks to rebuild pressure but the difference was immediate. It did blow some smoke at start up but it settled and drove perfectly. I've been running premium gas for the last 18 months with the occasional bottle of additive, but I'm going to start adding a half quart per tank of ATF. My tank is spotless, the lines are new, the filters are clean, and the dampers have been rebuilt. I think my MFI pump is the source of the crud. Its leaking oil into the valley and maybe only has one adjustment click left.