Does anyone have experience with fuel pumps on an 85 300TDT (260k)?

Someone suggested that it could be a crack in the block...is this common?

I am loosing coolant from the front of the engine at a slow but steady rate...~1/2 gal/300 miles. It is dificult to tell but it appears to be coming from the vicinity of the water pump. I think it may be the seal around the pump housing and not the shaft seal. I don't think it is a hose leak.

Any input or suggestions before I take the sucker apart .

Thanks for your time,
Alec.