Hi: I agree with the previous posts. Since you have a SS drip pan under your engine, just live with the rear main seal leaks, place and change an oil-absorbent "diaper" under the engine regularly. This is what we do with our c. 1965 4-107. There is NO magic bullet to completely stop rear main seal leaks in these engines!
These engines are strong and reliable. The Achilles heel of the 4-107 is the fact that the cylinder liners are wet, with o-rings to seal the water passages between the block and the liners. When the o-ring lands inside the cylinder block corrode and fail, then the engine is toast. Until that happens, don't let anyone talk you into buying a new engine!
As previously stated, ALL Perkins 4-107 and 4-108s had a split rear seal.
BEFORE you even think about dealing with "Dr. Diesel" at Foley Engines, do yourself a favor; search these threads and read all the horror stories!
Trans Atlantic Diesels in Virginia TAD for perkins engines, perkins diesel, perkins marine, perkins parts, perkins generators, perkins service
is an honest, reliable source for parts for your engine. (I am just a customer - no financial interest).
Your serial number can be found on top of the engine block, right above where the high pressure fuel injection pump bolts on. I lifted this from another site, and the info is accurate:
quote "The date of manufacture can be roughly determined by the serial number. Three systems of engine numbering have been used. The earliest engines had a serial number consisting of seven digits. The 4/108s were 73XXXXX, the 4/107s were 71XXXXX, and the 4/99s were 70XXXXX. On engines built during the early 70s the serial number was changed to include letters and figures. The number started with three digits giving the engine type, i.e., 108, 107, or 99, then a letter marking the country of manufacture, and finally several digits showing the order in the production run. My Perkins 4/107, made in 1974, is numbered 107U43112. Engines built in the late 70s and after carried an alphanumeric serial number of up to 15 characters showing the engine family, the specific engine type, the parts list, the country of origin, the production number, and the year of manufacture. A typical serial number might be ED1534U510256D. The last character, showing the manufacturing year, is a letter. B represents 1975, C is 1976, and so on through the alphabet. Letters I, O, and Q are not used." unquote