Federal Retiree and the MSC

As a Retiree from the FAA, if I went to work for the MSC how would that affect my current retirement. I have a feeling it won;t be for the better

You should probably ask OPM about that. I wouldn’t ask MSC, they’ll give the wrong answer every time. As a CIVMAR, MSC isn’t the same as regular civil service, I think they call it “selective service” or something. You can’t transfer in and out within the government as you can with regular civil service jobs.

MSC CIVMARS are “excepted service” I believe that’s the corrrect term. As a Military retiree, the only way it affected me was I earned leave at the new guy rate, those with military years but not retired got credit for those years and earned leave at a rate as if they had been working for MSC for all those years, etc etc.
As a FED retiree you should check with OPM