[offroadnt]

Accessory drive pulley seal, quite common on them. They are fairly easy to replace, sometimes the front cover may crack there also but haven't seen one in a long time.

 

[offroadnt]

It's been a few years since I did one and haven't been near the manuals for a month. The nut is regular thread, can't remember how I held the engine, might have given the wrench a hit with a hammer to knock the nut loose, didn't remove the radiator and I think I may have used a crank pulley puller to pull it off, I'm sure there are a couple threaded holes in it for the puller.

I'll see if I can get a break and look it up, it's not a big job and there are no timing issues and such you need to worry about. The engines I did it on were 444XTs in cabover Internationals and I think an N14 in a Western Star.