While testing the compression of the cylinder, I saw oil spreading across the floor. Looked and found this to be the culprit.
Well actually there seems to be a short and long version, cause when I asked for a sender unit for the oil pressure guage, he showed me 2 different pictures. One had a short pipe thread, the other had a little longer pipe thread on it.There is only one size. You have a gauge (all the big bell senders were for a gauge) and that is all you need to tell the parts store for a replacement.