Scott,
I shd hv stumbled into this thread earlier!
Have done 2 4x4s that had this problem before (some kinda hardened rubbery silicone
stuff that looks like those used on aquariums).
Not effective - MEK, Acetone, Petrol, Diesel etc.
Have tried em all. Forget the rotary buffers and other machines.
At last, a detailing friend in Hong Kong provided this unorthodox but dangerous sounding method. And he sent me that "dangerous thing" by courier.
Are you familiar with that round, stubby rubber door stop used in most homes, mounted near the floor? It could be black, pink etc in colour. It's just a piece of stubby hard rubber.
Find a way to attach that tubular/round rubber to a cordless drill with variable speed. You can use a small drill bit, and drill into that piece of rubber. I know it's crude...but hold on.
As you operate the drill, that stubby piece of rubber will rotate. Assume it's a gigantic dremel, and use that rotating rubber to abrade off those silicon bits from the paintwork.
You'll instantly see bits of that silicone-looking stuff flying off and falling to the ground.
Superbly fast and effective......but leaves behind marring marks that's easy to rotary-buff away.
Removing old door visors:
Also, remember when you had to pull out that old, faded plastic door visor, and it left behind loads of hardened, crusted old double-sided tape?
Solvents either don't work or takes too much time. Use that rubber-thingy method, and you'll realise it's the fastest method. After that, rotary buff that area using small pads+compound to remove any marring. After doing 4 doors, your rubber thingy would be partially worn away. Remove it from the drill, and by a new rubber stopper!!!!!!!!!!!!!!!
Yeeeeeehhhhaaaawwwwwwwwww!