I've been collecting those little silica bags from various things we purchased over the year, I had about a dozen, all into the P6 resting in garage. Must prevention?I may do.
get the musty smell out of the interior.
I used a variety of things, with fairly good success. A good cleaning, and I mean good and not forgetting the boot and headliner. Neutrodol, odour eater spray etc. And of course as you say, leaks and moisture. Warm garage helps.Doubt it.
You need to investigate any moisture getting in from glazing leaks etc. I never could get rid of the old car smell.