I have been a fan and proponent of using the neoprene type rear main seals (because they had less friction "for a little extra free power") since back in the late 1960's, plus I have also mostly used and recommended the FelPro brand. Recently this same issue has come up with severial other people when using the FelPro rear main seals in the early 144, 170, & 200 blocks (i.e. those that originally used a rope seal). Because of this continuing problem I believe that these latest seals are not being made to the orginal Ford Factory specs of the rear main seals like we're used or offered in the past, and or they may even be substituting a seal from another seal application. Anyway this is my theory and because this has now happened with quite a few instances there is definitely a recurring problem over the last approximately 2 or 3 years, of these rear main seal failures. But only by acquiring then doing a side by side comparison and accurate measuring of a new original Ford seal which I think is (C9AZ-6701-B) compared to one of these current FelPro seals will prove this theory.
At this time I don't know if there is another manufacture that makes the correct spec neoprene seal to fit these 200 blocks, so it is my opinion and recommendation not to waste your time installing one or the money to buy one of these seals that FelPro is currently offering. So It also my opion It's just best to use the old tried and true rope type rear main seal. Or unless you would be lucky enough to even find a "NOS" Genuine Ford neoprene rear main seal. To reinstall the rope seal you can make a replacement rear main seal locking pin for the main cap from the end of a small finish nail of the correct diameter and cut it off to fit into the main cap. Good luck
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