Here's photos of my evaporator and part of the evap case from my 92 300TE.

I could not find the leak with either my sniffer or with dye. Leak not big enough to have oil leak from evap case drains.

Also air did not come out very well from center vent. That vacuum element did have a leak.

I'll just replace all elements, evap, and blower motor.

I think it's pretty apparent that when you can not find a leak in system with dye or electronic sniffer there is a very good chance it's the evaporator.