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I would think the 4D55 uses the same filter as the 4D56.

I just changed the oil in my truck, I used a Luberfiner Filter LFP805.

You can also use Luberfiner LFP9930 or Hyundai 26300-42040 and 26300-42030.

This might be useful:

http://showmetheparts.com/luberfiner
http://www.luberfiner.com/content/where-buy

From their catalog, my truck takes the PH910

All Diesel Fleet:
1985 Mitsubishi 2.3 Turbodiesel Pick-up, 1983 GMC Van- 6.2 Diesel.
Benzs: 1995 E300 diesel, 1980 300SD, 1982 300CD, 1983 300D, 1985 190D.
1980 AMC Eagle Limited Wagon powered by: 3.6 Litre I6 VM Turbo Diesel Engine (one of fewer than 10 made, only 2 known to still exist)