I have rebuilt several Warn's and Ramseys they are all similar in the planetary design. If properly assembled, you should never get water in the gear case. My 8274 is a tank. I have never had it apart, and do not intend to until it dies.
The electrical components are another issue. You should clean your solenoid connections at least once in a few years. Check the communication wires for integrity. Remove the leads on the motor and clean any scum off with a small wire brush. inspect your power leads to the battery and make sure you do not have any rubbing issues.
On a side note - if you dont know which solenoid does what in the pack, label them with a a marker. Makes changing them easier.
As for cables, I dont care for synthetics. They are great for certain applications, but they dont fit my use. General care for either can be described as - In general keep cables clean and free of dirt. When winching, keep the cable out of the mud if possible. If you have high side loads be aware of bunching on the drum. You might have to stop, and re-spool. IF you do not you risk binding the cable in the which housing or bumper. After use cables should always be re-spooled onto the drum evenly. I like to set the parking brake on the first few clicks and monitor the wind as I pull against a tree. (With proper tree strap) Its a good idea to double check the point on the drum where the cable attaches. These are known for fatiguing and failing.
Synthetics are just like any other plastic and susceptible to UV degradation. Even applied UV protection will be removed once the cable is under load. Keep the line clean of any debris, and out of the dirt/mud. Use abrasion straps even if you think it wont rub. Consider buying a cover to keep the line out of the sun. Replace or splice when frayed.
Steel cables keep clean, and wound properly. Replace when signs of kinks or frays appear.