Slip rings can be trouble free or they can be a real problem. The slip rings on a yaw head are likely to be more troublesome than those on rotating machines.
With this non rotating application the ring must never open circuit, the rotation is slow and bounce shouldn't occur, mechanical accuracy needs to be good and brush contact pressure can be higher than on rotating machines.
The caliper type brushgear works well, things with brushes sliding in boxes don't fo so well in general.
If the atmospheric conditions are reasonable and the worst of the weather is kept out things behave better. Marine environments and other conditions where various chemical vapours are persent can cause serious problems.
For these slow rotating rings a film of lubricant can sometimes help to reduce corrosion of the rings, but in other ways it can hasten disaster, if the slightest break of circuit takes place the lubricant will make a very effective spark eroder and destruction will be rapid.
I have noticed little difference with ac or dc, once you get to the state where things are bad enough to sustain an arc then the game is over.
Well designed, construcetd and maintained slip rings can work fine for many years, badly designed or amateur codged rings are best avoided unless you live in a very difficult wind area where thisting cables is a serious problem.
Flux