I was just faced with the exact same problem on my '73 280SEL 4.5. In my ignorance I bought the aftermarket pump Autozone (or the like) recommended. It wasn't until I read Peter's post on flushing the old fuel pumps that I realized I had made a mistake. I took the old pump out, took the cap off carefully, worked it back and forth by hand until it broke loose, flushed it out like Peter said, and viola.

I am looking forward to putting my fuel tank in tomorrow and taking it (the un-named car) for my first drive.

Hope this helps
Paul

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Pxland

2001 Honda Accord

1995 Jeep Cherokee

1973 MB 280SEL 4.5