So thanks to Eddie for suggesting that I do the obvious (read the directions) without making me feel stupid, and Donna and others for their posts on other threads about silicone avoidance and how to apply pro-flex (I can't remember who posted the tip about dipping a finger in soapy water to smooth it - brilliant, thank you), I've successfully completed the fix for my leaky furnace vent.
I've had the
scamp long enough to have fixed a few leaky rivets but still approach drilling out a bad rivet with a bit of trepidation. The Suburban drawing of the internals of the vent and their connection to the furnace helped but until I drilled the rivets and pulled the cover I wasn't entirely certain what I would find. The lower vent is a loose fit and short tube and easy to remove as I pulled the vent cover out after drilling the rivets. The upper tube however is much longer and a tight fit. I was tight enough I was concerned about whether I could reinstall properly but fortunately it was long enough I could pull the vent far enough out to work on removing the old caulking without disconnecting the upper vent tube.
The cleaning of the old silicone caulk (from the scamp factory) was the major challenge. I spent several hours with wd-40, mineral spirits, goo gone, fingernails and a plastic razor scraper trying to get it all off.
After a final cleaning with alcohol I used butyl tape under the vent cover and after re-riveting with #66 rivets I used proflex to caulk the edges. Interesting that the Suburban instructions for installing the vent cover note that the edges of vent cover should be caulked and stress the critical importance of also installing a bead of caulk across the middle, between the two vent ports. Apparently the scamp factory does not read this part of the manufacturer's instructions as mine had no middle caulk.
Except for the nasty job of removing the old silicone it was an easy fix. Here are a few pics (sorry - orientation is correct on my computer, but they seem to get rotated when uploading) that may help others who encounter a similar vent leak issue. #1 vent cover pulled out showing both vent tubes; #2 lower tube after removal; #3 vent pulled far enough for working on silicone removal but upper tube still connected.