I just wiggled it and it came off. The washers under the nuts were very tight on the threads though, mabye that id your problem.
I didn't even replace the gasket when I did mine. No leaks afterwards either.

THREE nuts.

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Ash Peltier - tools, truck, tales
---------510-331-4118-----------
1982 240D - (272,000)
1998 Honda VTR1000F(RT) Superhawk Freeway (58,000) "Madrid"
1996 Toyota T100 4x4 (84,000) "Mary Kay"

Hmmmmm There may have been a difference between lift pumps on the NA & Turbo lift pumps.
Mine definitely only had 2 nuts and 2 studs and only 2 holes in the lift pump housing.

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.