I have a 1936 GMC and there was a zerk fitting on the UJBC as well, I replaced it with pipe plug. Don't have an answer as to way since your correct that grease is not to be pumped in.
The previous owner might have lost the original plug and just replaced it with the zerk fitting (using it as a plug) because the threads are the same: 1/8NPT.
Dean
Dean "Rustoholic" Meltz
San Leandro, CA
3511 posts on vccachat.org
Lurch -1927 LM one ton truck - tinyurl.com/Lurch-VCCACHAT-Gallery
Justin - 1928 AB Canopy Express (1/2 ton truck) - tinyurl.com/Justin-Stovebolt-Gallery
I believe a heavy oil like 600w was recommended and the early grease guns were able to use it so it made it easy. Until someone not knowing about the heavy oil puts grease into it.
Dave
My 1936 Truck has grease Zerks in places where gear oil is recommended. I don't think they have been replaced. Corn Head Grease from a Farm store like Tractor Supply is also a good choice for steering gears and U-Joint cavities.
Mike
Many Miles of Happy Motoring
3469 Posts on Old VCCA Chat
So do I need to take the housing apart to get the grease out and replace with Gear oil ?