I rarely come across Federal Pacific panels here in Alabamastan and any problems with them are the same problems that affect other brands of circuit breaker panels. I see dirt and the biggest problem, corrosion of the area where the breaker makes electrical contact with the buss. In new construction or remodels I will often use contact cleaners to get the construction dust off the connections. Something like Ideal Noalox can be used to re-lube the the contacts. On a lot of service calls I find corrosion and a soft bristle or brass bristle brush along with a spray electrical cleaner will clean it up. In some cases the stab is burnt and melted making it useless which is why I have kept old panels in past years so I could swap out the buss bars. Sometimes a new panel is less expensive than ordering new replacement buss bars if the old panel has a lot of damage. I have seen FP replacement breakers at our local big box hardware stores.
TDD