I am surprised no one has mentioned Meg`s Mirror Glaze No.40 Vinyl and Rubber Cleaner and Conditioner.
Me, I clean rubber seals around windows with Megs D101 APC or OPT Power Clean on a cotton swab (Q-tip) and then condition them with Aerospace 303 on another cotton swab. Makes a huge difference in how they look. At least when I wash a vehicle the next time the wash media does not get black streaked from badly oxidized rubber seals. I have learned to clean those seals FIRST with a old cotton cloth or blue paper shop toweling in diluted APC before my conventional 2-bucket wash with microfiber noodle pad as my wash media if I`ve never washed or detailed that particular vehicle before.
Rubber seals around moon/sun roofs take a beating. Unless they are taken care of on a regular basis, they tend to crack and weather check eventually. The seals around roof seams or the water gutter/track can be problematic as well.
What is surprising to me is how much dirt and debris (like decayed leaf or lawn litter or pine needles) gets trapped into door seals or door jam seals or rear hatch/trunk jam seals. The folds and channels hold a lot of that grime and if they are not lifted or gotten under or between, they remain dirty. Q-tips and blue paper shop towels are good for this cleaning task and as they become soiled and blackened, they are disposable.
A good example is the folded V-seal at the bottom of some Ford vehicle doors. Take a cotton cloth or paper shop toweling soaked in diluted APC and try cleaning in the fold or V. Then you`ll know! No one sees it and because it`s at the bottom of a door, few clean it.