You really have two questions here. As has been discussed, there is a vacuum leak somewhere. It's not necessarily in the transmission circuit. If you look at the pump, you will see that the brakes and engine shutoff are fed with a large plastic hose that attaches with a flare nut. Next to that, there is a small vacuum line that fits into a nipple. The small line feeds everything else in the engine compartment. Just start there and test at each branch with your mityvac. You will find a leak. As a matter of best practice, if you have one leaking elbow, Y or connector, then you have twenty more that will fail soon. If you don't want to be doing this often, get a full set of connectors and go to town.

As for the pump, I replaced the one on my 602 at something over 300K miles as a preventative. If you're getting up there, keep your eyes open for a deal and do it for peace of mind. There is a Chinese copy of this pump, but you want to look for the real Pierburg pump.