Large Advents (1974) woofer pops with deep bass.

Before surgery/replacement try rotating the faulty woofer 180 degrees.

The woofers also need to be sealed to the cabinet (it's a sealed system and any air leakage will increase the woofer's travel distance/excursion).

Once snug the bolts should be tightened systematically and gradually (like tightening up the oil pan on a car).

I don't know what would be good to seal them with (RTV silicone?) but others here should know.

DeKay

Here ya go!

 https://www.simplyspeakers.com/advent-replacement-woofer-p001-31858.html

Uh, considering they're almost 50 yrs old you may want to consider buying something newer ...

Uh, considering they're almost 50 yrs old you may want to consider buying something newer ...

Yea, if the speaker driver is 50 years old, it probably needs new surround’s, however you can get replacements online usually at pretty good prices. Check out Dayton. I’ve used their woofers in projects a couple of times and been very happy.

All the best.