The GMC CCKW

the crankshaft seal, front and rear are dripping oil, not large quantities, but engine sump is constatly wet and when stationary there are always few drops on the ground, but on 200 mile journey there are hardly need to top up.

Since those seals are of ancient design is it worth to bother changing them ?? The old trucker told me that this type of seals just have to drip oil, when new they tight but that lasts only for a short time, he also told me that with old trucks what they used to do is to weld some sort of pan and mount it under the engine so Police wouldn't harass them about oil drippings.

Hi
Just be 100% it is the front & rear seals leaking, I had a CCKW that used to leak oil, it appeared the rear seal but in fact was the rocker cover gasket leaking! and running down the rear engine block, was not obvious until close inspection.

Regards

If it is the valve cover, clean the head with gas and glue the gasket to the head only with gold Permatex gasket stuff and install the cover to hold it in place overnight. You can then take the cover on and off and the gasket will stay put. The top of the head is flat and any leak on the velve cover gasket will let the oil roll right off especially in the rear.

of course the top valve cover can leak but this is not the case, since I wiped engine few times I am pretty sure leaks are generated in the crankshaft/oil pan are, if I remember correctly there are felt and leather seals there, I am not sure about front (the pulley side) but in the flywheel side in order to change leather seal the crankshaft has to be removed so its not a easy job,

as I mentioned earlier it is not like huge oil loss, just this weekend I did 250 miles, no need to top up, but the oil pan, flywheel cover, gearbox and even transfer box are all greasy because of oil drip, so I wonder should I bother with new felt seals or just keep wipeing time to time and not bother

Hi Jakub
did you ever get an answer to this post? ... because my vehicle is doing the same ....

No, I did not get answer, but after careful observation my conclusion is that problem is negligible, the amount of oil dripping is next to nothing, few hundred miles require topping of 1-2 liters, nothing to worry about, apart from some stains on the driveway and moaning wife

The rear main seal is usually what is referred to as a rope seal. I think originally they were graphited and are of a woven construction. They are in two pieces, upper and lower. The lower half is in the main bearing cap and is easily replaced. The upper half is in the crank case and requires crank shaft removal to do the job properly.
I was helping a friend assemble a Chevy stove bolt engine on one occasion and we needed to procure a rear main seal as there wasn't one in the gasket set. We went to an old time parts dealer and told the fellow what we wanted and he returned with only one half. We said, "no, we need two of those" and he said, "what? For one engine?" His response made it obvious that for his entire career, people have only ever replaced the lower half unless doing a complete rebuild where the rear main seal (two parts) is normally included in the o/haul gasket set.

David

David
will replacing the lower seal solve the problem ...or only very temporarily?

I really can't answer that question except to say that it must improve the situation even if it doesn't completely cure the problem.

David