Earlier this year, I ran the RR through White Pine after White Pine for about 3 weeks straight. These were heavily storm damaged trees, oozing more sap than I'd care to remember. I was washing ropes 3 or 4 times a week. Nothing in my experience could have been cleaned and brought back to original performance characteristics better than a mechanical device. Cleaning the RR is easy, and when rebuilding, I have lubricated crucial areas with a dab of olive oil.
If you hit a dollup of pitch, you will feel a difference, for sure. At 100', I found the most comforting technique was to mitigate weight on the RR to ease it past the stickiness. I would do this by standing on structure if it existed, or grabbing a foot lock with legs more extended and easing into a sit.
All this being said, pitch buildup would have to be considerable and localized in order to create an issue. Otherwise, performance was quite normal and predictable over minor "contamination".