do i need a new steam boiler?

Question

keeps losing water, and it shuts down. a lot of rust in sightglass

Answer 1

Well first thing is the system needs to be drained to get rid of the excess rust. SInce you aren't listing leaks as a problem, I must assume the water loss is via steam vents at the radiators?

If so, the regulator valve may be rusted or worn out and unable to refilll the system automatically. This is best serviced by your heating company or even a plumber.

It is most likely shutting down from low water, so if you solve that, you should be good to go.