Late 617 Turbo Main Fuel Filter Bolt O-ring Seals x 2

For reasons of hoping to solve fuel filter leak problems Mercedes changed the center bolt design in some 1984 to 1985 model 123 300D 300TD 300CD and 126 300SD. Instead of one o-ring on the bolt they changed it to two orings (as shown iin the picture. Problem is it is not possible to determine which bolt you have unless you remove it. A copper or aluminum washer under the head of the bolt will give you a clue you may have an older bolt design - but not for sure! I have seen some actually place a washer under the head of the bolt that has two o-rings (and this is not necessary)! The larger o-ring is particularly hard to find.