1983 300CD

I replaced the external check valve a few weeks ago because the internal plastic piece and spring were missing. I didn't see the missing pieces inside so I just replaced the check valve. Then I was having intermittent vacuum loss, so I pulled the vacuum pump off the car. I disassembled the vacuum pump and found the missing pieces inside the little pocket behind the nipple where the external check valve screws in--not knowing the internal layout of the vacuum pump, I was worried that they had churned through the engine--yet another smart design from MB. I think these pieces were blocking the vacuum in certain instances, causing the intermittent vacuum loss I was experiencing.

Anyway, I completely cleaned out the vacuum pump while I had it off, which included cleaning out the oil inside/behind the piston. Now I need to reinstall and I'm not sure if I should prime it with oil or if the engine sends it oil once it is running.

Thoughts on if/how to prime the vacuum pump/piston before reinstalling?

Thanks.