71 year old boiler

[MisterRogers43]

Hi everyone! I have a 1953-ish oil-fired Yellow Flame Model 50 boiler installed in my house. It's rarely been serviced, and it shows. I drained the expansion tank because the PRV was filling up a Home Depot-sized bucket with water in the span of 2 days! And I also adjusted the draft control because it rotated both ways. Anyways, the issue is that the boiler is still leaking from the PRV, perhaps a bit less water, but it still is. I heard that flushing the boiler can help with that, but there's a problem: the old Weil-McLain Pressure/Altitude/Temperature gauge does NOT work, so therefore I can't expect to properly refill the boiler to a safe pressure since I can't tell what the pressure is at. So, my question is - Is there anything left that I can do? Or is it time to call a professional?
Boiler Pics

 

[Fitter30]

Leaking from the pressure relief valve? Manual fill? Cast radiators? Boiler drain have a garden hose thread?

 

[Sponsor]

 

[MisterRogers43]

Yes to all of the above!