Dealt with them? Most of the experienced/immersed people here have bought from Jess for decades for sure and many try to avoid them based on their reputation. Good, unique, stuff, but...
Patience. Yes. Now, you did the right thing asking if the part you wanted was in stock -- that's half the battle and the days you might have thought it will take will only be weeks... if they were correct. They are truthful I believe, except for saying the Newtown Musket was a matchlock (it was a snaphaunce first) but are awful business people... The worst!
Getting a hold of them? LOL Getting the right part? The first time -- really!? Being told they sent it to you already when they didn't? Good chance.
Good luck.
Like buying from my good ol' boy friend at TVM, I wish you could always see, hold, the item in person before you gave them any money not to have any issues...
I have one gun made by them that took 12 years to get finished. That probably isn't the record, but it could be.