other than keeping car garaged, regular cleaning, what do you guys use to maintain your car rubber (around windows, doors, t-top seals, etc.) and interior plastic? (this is for my 1997 z28)

 

For the weather strip rubber, I spray on silicone lubricant spray. The brand doesn't particularly matter, but WD40's silicone spray is easy to find. You spray it on and wipe it off with a paper towel a few minutes later. It will take some black crud off with it which might scare you, but for yearly maintenance, I have never seen harm come from it. Silicone is a dry lubricant, which means that once it dries, it still provides lubrication, which is why it's good for door hinges in your house. If you are scared of it, you can use Meguiar's Tire Spray. One of the types they make specifically says that it can be used on weather strip if I remember right.

For the interior plastic, it really depends on what is wrong with your plastic. If you aren't a smoker, don't eat in the car, and don't drive with the windows down, you can probably get away with just spraying Meguiar's Interior Detailer spray on a microfiber towel and wiping everything. If your interior is dirty, you might need to use a little car wash soap in a bucket with a rung out microfiber towel and wipe everything down first. You'll have to be gentle given how old the ABS plastic is in these cars and not be very aggressive or put much weight on anything.

If you have any cracks in the ABS plastic (the hard plastic, not the soft), you can apply Same Stuff https://www.micromark.com/SAME-STUFF-APPLICATOR and it'll join the two pieces back together, eliminating the cracks. It'll leave a little bit of a snail slime appearance, but it's better than a crack. It will not work as a glue and it won't likely save UV damaged ABS (which is very brittle), but it'll fix accidental damage cracks (like from taking things apart...) if you happen to have any. It works really great. It's made for plastic model cars (which are often made from ABS) and our 4th gens have a few components made from the same type of plastic. Technically, in theory, every interior plastic in a 4th gen had a UV clearcoat of some kind on it when new, which is why the surfaces had a dull sheen to them unlike completely untouched ABS plastic like a model kit.