About VTS issues. I have 4 XP's and have had to rebuild 3 of the VTS units. There are two levels of problems. If the boot on the shaft fails than water gets inside the unit and can damage the small drive motor. However, I have found that the damage is usually limited to rusting of the exterior and soaking the motor in HD paint thinner will get it going again. The worst outcome is failed electronics. This can be repaired but takes time and talent because the electronics are sealed in the box behind the egg shaped motor enclosure. Usually, what happens here is one of the two relays goes bad or becomes disconnected from the circuit board due to water getting under the sealant and corroding the printed circuit board. The relays are controlled by a simple bit of electronics which seldom fails (unless connected incorrectly). From what you describe, clicking in one direction but not the other, suggests that one of the relays is not closing. You can attempt to make the repair by heating the potting material with a heat gun and carefully carving it away. You will see in the middle of the board the 5 pins for each relay poking up through the board. Try cleaning and resoldering the pins. The theory behind the electronics is as follows: There are two relays, one for up and one for down. These relays convey (relatively) high current from the red power wire to the motor. The relays are activated by two low current circuits that responds to the up-down button. When the button is pushed one of the circuits sends current to close its relay and thus send current to the motor. There are about a dozen magnetic switches on the other side of the board that limit the distance the motor can drive the shaft and which respond to the position of the drive shaft. These can fail but probably not your problem.
You can test to make sure power is getting to the relays by using a volt meter. Hook the meter ground to the negative term on your battery. If I recall correctly, one of the pins on each relay is always hot with power coming from the red power lead. You should be able to get a 12v (hot) reading off that pin on both relays. Now have someone hold the up-down button in one position. You should find that a different pin on one of the relays is now hot as it has been powered by the low current circuit. If you move the button to the opposite position then the same pin on the other relay should be hot. The pin that gets hot by pressing the up-down button activates the relay and sends current across to another pin that is connected to the motor.
If unpotting the back of the circuit board (the back is what gets exposed by removing the potting) and checking for corrosion does not fix the problem (the relays don't function) then you have a much more difficult fix ahead. One that I cannot begin to explain here unless you are ready for a firehose treatment. If you need more info please let me know. If you succeed in fixing the problem then great! You need to repot the circuit board or worse things will happen. I suggest using some acetone to thoroughly clean the board and box. I line the space with very thin plastic sheet then fill the space previously occupied by the potting material with clear epoxy to form a solid lid. After the epoxy hardens I peal off the plastic and have a nicely molded lid for the box. I use RTV to glue this in and seal it from moisture. That way if anything goes wrong, I can see the PCB (like a window) and open it up if necessary.
