'96 Dodge Caravan

I have a '96 Dodge Caravan with 188,000 miles on the engine and transmission. The transmission has just started some minor slipping. Is there anything I can check or replace before it gets any worse? Any magic additive that could extend the life? The transmission is a 4 speed automatic.

In my experience the only magic additive is money. Which I would add to a bank account to start the fund to buy another vehicle soon, as this one is probably reaching the end of its serviceable life. Obviously you should check the level of the fluid in your transmission.

Yes, you can check the level, the color, and the odor of the transmission fluid.
If the level is low, you need to refill with the correct spec fluid. The Owner’s Manual will tell you what type of fluid is necessary.

If the color is anything other than red, and if the fluid has a “burnt” smell, that is an indication that the transmission’s days are numbered.

However, with the number of miles on the odometer, I suspect that the transmission is just plain ready for a rebuild. And, if it was not serviced as it should have been–fluid and filter change every 30k miles/3 years–it is actually somewhat amazing that the transmission made it this far before beginning to slip.

As long as the problem is not merely low fluid level, I strongly suggest that you take the vehicle to an independent trans shop for evaluation. Do NOT go to AAMCO, Lee Myles, Cottman, Mr. Transmission, or any other chain operation unless you want to be charged for a rebuilt trans whether you actually need one or not. An indy shop that has been in business for at least 3 years is more likely to give you an honest assessment, a lower price, and far better workmanship.