My 1990 W126 (560 SEC) still has its original R12 aircon system. But it has a TINY leak. The gas is low - indeed almost empty; and a nitrogen pressure-test confirmed that the circuit was very s-l-o-w-l-y losing pressure. Can't see or hear where the leak might be. It must be a pinhole, or possibly an ageing O-ring or seal.

Now...I have a limited quantity of R12, which I'd like to use to refill/top-up. But I don't want to use or lose any of this supply in trying to trace the leak (eg with dye). Is there any other way of tracing the leak without using up precious R12, and equally important, without polluting the aircon system with anything which might be incompatible with an eventual refill - once the leak is cured - of R12?

br1anstorm