And sometimes the joint is so impacted with old grease and rust that you have to disassembly it to clean it. You might even find that both bushing are worn out. Items #2.
The zerk is a 1/4-inch-28 Straight Grease Zerk - JD7844. Easily obtainable as at sources mention above. The bushings are about $12 US each.
Thanks for the information! The diagram is super helpful. It's nice to see all the parts involved.
I'm hoping that replacing the grease fitting will put be back on track. If not, then I'll do as you suggest (disassemble, inspect, replace as needed, and clean).
I purchased the mower in 2012 at either Lowes or Home Depot (not sure which place). I've been very good about changing the oil (Amsoil 10W-30) and filters, but not so much with anything else. I wasn't organized at that point in my life, nor did I have a place to work on my equipment. I now have a well-organized heated garage. I'm also gaining the necessary tools to do all my own maintenance.
The D100 has been a great machine. I'm not using it to mow residential lawns. I've been using this mower to develop virgin mountain property by mowing down weeds and native blue grama clump grass. Most people will tell me that I bought the wrong machine for the job, but so far, it's lasted 139 hours and 9 years! I bought the mower new for $1,200 dollars, so I'm not complaining.