Hey Mike
Here’s another thought that it’s likely someone will comment doesn’t apply to C-34s, or isn’t germane to, or is pontificating about your unfortunate tower situation

When we check out the condition of the (sometimes just wet, sometimes rotted) wooden plank buried in the c30 keel stub, we drill down thru the bilge w/a 1/4” bit, into the wood and extract/inspect the chips (dry - wet - rotted.) You could do the same because you’re already “committed” to covering/fixing the surface.
IIWMT (if it were my tower) I’d start with the screw holes, progressing in a pattern depending on what you find each time. You might find the lay up is competent in all but a few spots that could be treated by using infusing penetrating resin. At least you might define ahead of time what spot(s) need to be gouged-out if it’s more widespread. Of course, it would also define whether the box is vacant below some depth or fully occupied.
Is what you’ve found so far matching with this approach?
If that approach makes sense, lastly depending of course on the findings/extent, I’d drill a series of holes outside the tube circumference and inject penetrating resin to make sure that crack leakage is fixed. Could be in conjunction with Dremeling out the crack(s) and injecting resin from inside the tube (attacking the attack from two directions as it were.)
IIWMT (no need to repeat) I’d drill it incrementally — based on “chip feedback” drilling to the core level incrementally to determine both the extent and depth (if any) of the rot layer. You may find (makes sense) that it’s all laying down at the “deck level.”
How tall is the tower (realizing of course, that I’m opening the door for continuing personal attacks because I should have bought a 34 so I don’t need to clog up the forum with such silly questions about it’s construction.) Can you reach to the crack level with a jobber bit or would you need an electrician’s bit? Whatever length, I’d mark it with BRIGHT

tape so you reach to the core level and hopefully not thru the headliner.

)
Gee I wonder what the negative feedback will be this time?