Nikon D80 Autofocus Lag?

So, I have somewhere around 200k shutter actuations on this camera, which I recognize is pretty good. I baby this camera, that is why it has lasted so long. The autofocus is going, not bad enough to not be able to photograph a baseball game, but I photograph skydiving landings from the ground which means starting to track while the jumpers are approximately 600-800 ft up in the air, going over 40 mph. When the jumpers are in their turns is usually when I catch them, so they're spiraling and the autofocus is just whirring and increasing/decreasing depth of field and not catching them in time, this was not a problem 1 month ago at my last event. I'm wondering what I can do to try to fix the autofocus or if anyone knows approximately how much it would cost. If it's not worth fixing I'll find a replacement, but right now that's not easy, so the cheaper the fix is, the better.
If you can link to a tutorial that would be amazing.

If you can focus properly on a bush, then you may have a focus mode setting issue. It's easy to disturb these settings if you aren't familiar with the settings. For instance, if you select single point focus mode, you could be focusing on the sky which will not lock focus.

Perhaps set it up as follows:
* Focus area selection: Auto-area AF (page 87 & 30 in your manual)
This will automatically select one of the focus points which will probably work well for skydivers.

* Autofocus mode: AF-C (page 29 in your manual)
This will continuously track focus on moving objects.

These can be set via various dedicated buttons on the camera body (i.e. You don't need to swim through menus).

Set your autofocus to spot. If your current focus area setting is matrix, there's a lot of empty sky and the camera does not know what you are trying to focus on.

Most compact cameras can't even focus on clouds since they use contrast detect. DSLRs on the other hand use phase detect, and they can focus on clouds, which may be happening when you are trying to focus on a skydiver.

So, if you use spot focus you select which point you wish to focus with. Then simply place that focus point over the skydiver and focus.

And the other advantage is you can also use spot metering when you use spot focus. Spot metering is useful here as the bright sky will tend to fool your camera into underexposing the skydiver. By limiting the exposure reading to spot and placing it over the skydiver, a more accurate reading can be done.

(I bet you are currently having to use manual exposure or exposure compensation to get the correct exposure)

Anyway, a couple of things to try. Search for tutorials on using spot focus and spot exposure area rather than photographing skydivers. You may get more info that way.

It is the same issue at air shows. The camera wants to continuously hunt as the aircraft is small compared to the sky. You can either use spot focus, or I have even went to manual focus and stopped down the aperture for a wide enough depth of field to compensate a focus area. However, this is due to tracking high speed aircraft. I think skydivers might give you a bit more time to setup each shot.