Don:

I know your '92 is configured differently than my '91 in several ways, and I think the A/C systems may be totally different, so most of what I have to say may not apply. But - in my minimal experience with working on A/C systems with a more knowledgable friend, I've found the most common source of leaks are the Schrader valves at the service ports. You can buy these at Auto Zone or wherever for less than a buck apiece; they're supposedly generic. Replacement requires evacuating the system, however. Also, on my '91 740T there are three places where you can open up the high side. One on the back of the compressor (closest to the engine, furthest from the fender), one on the pipe coming out the bottom passenger side of the condensor, and one on the receiver dryer itself.
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Mike W., four 240s, a 740T and a 940T, Largo, FL