Sealing ducts & removing old duct tape

[St. Joseph]

My ductwork is of the rigid, sheet metal variety, located in the crawl space of a 1966 ranch. I was surprised to see that the old style duct tape is holding up pretty well. On some joints the duct tape is starting to come off, however; and there are no screws holding the joints together — just the duct tape.

Here's a link to a short video of my ductwork.

My general plan is to seal the longitudinal seams, as well as the joints (elbows), with foil tape, and then brush mastic onto the elbows.

So, here are my questions:

1. Should I remove the old duct tape, even if it's still holding up?
2. I know that sheet metal screws or some other kind of mechanical faster is required under building codes. But for a DIYer, can I just use the foil tape and call it a day?

Thanks!
St. Joseph, ora pro nobis!

 

[Dirtmechanic]

No it is under pressure. The mechanical fastener holds it together while the (they make mastic tape btw) seals it up.