Hey Jerry and Fox...
The replacement motors come with a plug now to cover the hole. I have used a home made plug in the past, but it just seems the quality of these motors might be the issue now. I believe they probably do well on there side (horizontal) but not so well when used upside down (vertically).
I do remember seeing a rubber vent tube in the past (I have had these years trucks for over 30 years), but haven't in a while. I wonder if that would vent and also help prevent water from seeping in???
One more comment to Hambone... Another reason I know the heater core is not leaking is the fact the defroster works as expected. Usually if the heater core is leaking, it will fog up the windshield when the defroster is on.
On a side note, the replacement "original" blower motor I found seems to be working for now, but it is making noises (age?) and I expect the need to replace it so I bought another new blower motor which came with the plug, so the mystery will continue... I guess I am getting tire of replacing the motor every year or every other year at the start of fall when you tend to need the defroster.
