Isn't this stuff supposed to be keeping the water from doing the nasty in hard to see places?

Anything particularly good out there to fix this, preferably in small quantities?

 

Yep, the old stuff they used to use eventually reaches the end of its life, becomes brittle, cracks, rusts beneath, etc. Here are some options from low to high:

The cheapest option would be to get some Acrylic latex caulk for a couple bucks at a home center. I like the acrylic latex as an inexpensive product b/c it paints over easily.and holds paint a long time unlike a lot of silicone calks. It also happens to be the cheapest. The next step up that I like, would be a urethane caulk. Urethane paints ok.

If you want to do a more 'pro' job, 3M makes a seam sealer that works pretty well. It cures by atmospheric cross-linking ...so it takes a few days (or more) to harden. But it paints up well and is the most like the OEM product. Comes in a tube or can.
https://www.ebay.com/p/1511804363?ii...xoCxMgQAvD_BwE

A urethane equivalent:
https://www.ebay.com/p/1511804363?ii...xoCxMgQAvD_BwE

Then there is the absolute 'best' product, which is a 2-component seam sealer. This stuff is absolutely amazing. It's what they would use at the factory on new vehicles, and body shops. It's superior to caulks in every way (strength and flexibility) ..except price. The special application gun alone (3M) is eye-wateringly expensive. But it is the best. There's a self-leveling product too. And truth be told, you can just push it out of the tube by hand with a deep well socket too ..don't necessarily need an application gun.
https://www.ebay.com/itm/3M-Automix-...cAAOSwSXFdxs5-

 

Not sure if one of these knockoffs would hold up long:
https://www.ebay.com/i/202047262194?...yABEgKAsvD_BwE

 

I hadn't see that application gun. Lot cheaper. Thanks for sharing.

Couple other thoughts:
1) If you DO replace the caulk, dig it out and completely clean off the rust and or dirt. Then spray a couple coats of a zinc-chromate primer over the clean metal.

2) I'm not a big fan of the 3M seam sealer like #8405 (my first link above). I goes on fine and looks good initially but I've had several instances where it gets hard and shrinks in like 2 years and start cracking. The urethane equivelant is probably much better (but I haven't used it).
3) The two-part products absolutely won't shrink or crack, and they cure fast. The self-leveling works great on water drain channels (roof), but will run off vertical surfaces (so use the 'firm' product there).

 

Just from looking at several ads for those guns, seems like you have to watch what capacity they are listing. The 3M two-part you listed says 200ml(?) but some of these cheaper guns list a lot lower capacity. Not sure how that shakes out.

 

i kept wondering where the leak inside was coming from, i looked under the dash above all the wiring and i see a rotted spot with a stream coming out of it, i i tried everything to make it to that spot but its inside the body behind the fender, i felt like my chipped old caulk was the cause following the rust paths so i chipped it all away ruffed it up with sand paper and took some NP2 caulk from work and slicked it on there trying to channel the water back tword the fender drain

 

that how is how my floors rotted out and the bottoms of my doors was from dry rotted window seals

 

https://www.homedepot.com/p/Amerimax...5148/100011940

This is what I just used to fix up my floors. I'm happy with how it laid out and the price is good. People who are into restoring cars use this stuff with good results.

 

Likely going to chip out what will come off, and go with a urethane for now.

 

Another thing, a HF chisel set was easily worth the $7 to remove some seam sealer, also goo off.

 

man your beep is clean

 

My PPG paint jobber has the urethane in white for $20 and change.

 

Clean up and repair. Hopefully, that engine compartment will stay over 70 degrees long enough for this stuff to get happy and cure.

Driver's side, before.

3M 08368 (white urethane) $20 and change at the PPG store.

Driver's side after.

Passenger side. Cleaned up with the help of a Harbor Freight 1/2" chisel.

Scuffed with 220 sanding film. Cleaned with CRC Electric Parts Cleaner

Eat your heart out Toledo!