Injection pump leakage

[wiltronix]

Looking for service manual for FIAT 55L crawler tractor from the 1950's
Mine is in need of TLC and I have no service information for the old girl
Only 4,000 hours on the clock but I notice heavy leakage from the fuel injector pump.
No name plate on the pump, only a serial number.
Leakage from a port beside the prime pump turns into a continuous squirt when engine is under heavy load.
Any ideas?

[MrF]

I dont know this pump or tractor, but if it helps this seems like a thoroughly well detailed picture resto of one with lots of technical data, but in italian.
http://www.iadermotoridepoca.it/fiat55cl.html
I think in there it says it has a fiat PE4B80D diesel pump which is a bosch pump made under license. You might glean some other useful info from the pages too, like injection amounts and timing etc.

Also typically when I have seen a actual squirt jet of fuel, its been from a bleed port when a tipped screw is removed, could it be that this has backed off/come adrift/been lost somehow?