Never seen one of those lines plug. What is it plugged with? Is it pulling something from the trans?
I have also not seen lack of vacuum change shift positions on that trans. Lack of vacuum to the modulator just produces harder shifts on 722.3 trannies. Shift timing is dealt with through the control pressure cable; which is known to stick both in the housing and in the valve body.
The most common intermittant is a bad kickdown switch under the gas pedal.
Bosch Master, ASE Master, L1
33 years MB technician