Reddit mentions of Liqui Moly 2005 Diesel Purge - 500 ml

I'm not a professional mechanic, but I have an '83 240D, and here's a few of my tips:

Have you done a valve adjustment? This can make a huge difference on running smoothness. It's not too hard of a job, but I would recommend having a second set of hands. It's nice to have someone with the feeler gauges at the ready to measure while you still have the wrenches on the adjustment screws. You're going to want the special wrenches like these. Usually you can get them on ebay cheaper.

I like using the Diesel Purge product. Pretty simple to do, and only takes a half hour or so. There are quite a few YouTube videos out there about how to do it on a w123 chassis. Change both fuel filters after the diesel purge.

Differential fluid is easy to do, but being you're in the salt might make cracking those plugs difficult.

Cold starts with diesel are always fun, but just a simple thing is when were the glow plugs last replaced? If you're doing the valve adjustment, you're already in teh general area and might as well change them out if it hasn't been done in some time. (Some people say they get 200k+ out of them.) Be sure to get the glow plug reamer as well to clear it out and get that carbon out of the threads.