I took in an old muscle car with a sticky speedometer. The owner first showed me the impressive broad collection of gauges, and showed me the differences between Mustang, VW and GM gauges, and the tamper-proof odometer systems. He quickly disconnected the speedo. cable from the transmission and clearly showed me the nature of the speedometer's stickiness. He rebuilt my speedometer and car was ready a few hours later. The speedometer works perfectly now. I appreciated their explanations as well as the expedience in the work.
Pros: Expertise in the field, Inventory of many parts, fast
Cons: It's not cheap (but all specialists will be pricey)