You pretty much answered most of your own questions.
The guy making the pump rotors is Brian Wilcox. Call 810-794-7685 before 8 pm est please. Or email Baron0418@att.net. please note the b must be a capital. Your diagnosis is correct, the old one is swollen up from grease, as expected. They all have a grease seal problem. I have a fix for that which I can post if you’re interested. Water discharge is not directly connected to the slots, but merely blows out of them when running.
Starting instructions say hold the primer 10 seconds, then release it and start it. I use a slightly different approach. I hold the primer till the bowl starts to overflow, then release it to the richest knob setting without engaging the primer feature. Start motor and adjust knob to best HS running position. Then remove knob and reposition on the needle so it points straight up. Experience shows that will be roughly 3/8 turn open from closed, and of course further open while priming. Yes, it helps a lot to have it somewhere near level, or even tilted slightly back.
Have fun with your project. Warning, they can be addictive. I think I have somewhere around a dozen of them. Lost count.
