More car trouble (minor but hard to solve)

Last week, I took my car into the shop to get an oil change and a degreasing, which the garage recommended to find an apparent slow leak somewhere in the engine (which means I have to drive around a few hundred miles’ worth so they can see where the dye they put in leaks out, but I drive so little that that could take months), and also to see if they could diagnose an intermittent clicking or tapping sound I started to hear, which I thought might be something dripping onto a hard surface, possibly connected to the leak. Instead, the clicking turned out to be the result of a cracked gear in the HVAC system, part of the dial mechanism that switches which vents the air comes out of — which apparently rotates even when the fans are off, I guess, since I turned off the air so I could hear the clicking better. Unfortunately, my car is 25 years old and that part has been discontinued. The garage guy tried ordering a substitute, but it didn’t work, and he spent hours searching for an…