There is a procedure described in this TSB using a smoke machine, in many cases we need to go this route when you can not visually see the leak.
DIAGNOSTIC PROCEDURE FOR LOCATING LEAKS WITH THE ROTUNDA'S VACUTEC - 522 SMOKE LEAK DETECTOR MACHINE
I already know this and will be preforming this test. This can't be the first time that this has occurred with this model so I'm asking what has been found to create this situation that puts me on a more direct path to getting this resolved.
I can not say I have seen any thing in particular, if you use a piece of vacuum hose about 3 feet long one end to your ear and the other used as a probe you might be able to isolate it. Or even use the carburator spray method and try to isloate that way.