I've just fitted a Sparex bottom gasket set to a Fordson Dexta with a Perkins 152 engine. I had a lot of problems with the front and rear cork seals for the sump(oil pan). The proper cork ones are awkward to fit at the best of times. But they do normally stay in place. The Sparex ones were made from a different material which was stiffer than the cork ones and would not stay in place. All others that I have used have been parallel. The Sparex ones had a width variation of 055"....something that was quite visible. It looked as if someone had cut them by hand with a sharp knife. To fit these seals I had to cut pieces of wood to hold the cork ends in place whilst the cement went off overnight. I have rebuilt dozens of engines in my 40 years experience with MF and others and never had to do this before. Needless to say I won't be buying any more Sparex gaskets. Check also the material that the rear crank rope seals are made from. It is a far stiffer material than the original. I have had two which have failed after about 5 hours work (not Sparex ones) and have fitted a genuine Perkins one to this Dexta.
DavidP, South Wales