[joejoe1]

You do need a black light to see u.v. dye. However if the front seal is leaking you will actually see it drip from behind clutch area, and it will be obvious. On my '84 I found the leak was the schrader valve for low side. It can be replaced with compressor on car but is very tight. and belt needs to be removed to get access. (also from picture you need to replace belt as it looks to be fraying a bit)

When I ran across a bad a/c shop I decided to do my own work, and invested in much of the equipment needed (only need gas analyser now) If you have access to an electronic sniffer (maybe a friend has one) you can narrow down possible areas very quickly. Problem is the system can leak from any of the 'O' rings throughout the system. Some of the areas are front seal, schrader valves, connections to receiver dryer, connections to condensor, high/low temp sensors. Where you REALLY do not want a leak is from inside car, as replacing that condensor requires removing most of interior.

Lastly did the shop say they added dye? If so then they should also have the black light to check and should have. The system does not have to run long to pressurize enough to see leaks. Hope tis helps some.