One of the best diagnostic characteristics of using the florescent dye is that absolutely pin point accuracy can be had in how the leak exists.

The fact that you are seeing an indication without a "blacklight" means that you have a great stain. Now you need to have it viewed with a black light. If the leak is coming from the speed sensor, the manifold or the line fittings then I would just reseal. If it is leaking from a body seal or the shaft seal I would replace the compressor with a rebuilt unit from MB. If its a shaft seal and your tech feels confident then its a decent possibility of a cheaper fix. It is a labor intensive job and the seal is pretty pricey from MB and there is a significant chance it won't work but due to your low mileage, its a reasonable repair.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician