The output on my sand filter developed a leak. I think it's a seal that
needs to be replaced or cleaned and lubed but I need to get the coupling
apart to fix it.

It's 29 years old so the plastic is probably very brittle. Does anyone
have experience with removing the coupling and repairing the seals?

Here is the coupling:

http://www.safaricabs.com/output.jpg

It's a BakerHydro sandfilter.

Here's a blow-up:

http://www.poolcenter.com/images/8bakerii1969-83.gif

another:

http://www.poolcenter.com/images/8bakerII_hrv1984.gif

I'm real worried about the coupling breaking when I take it apart. I'd
rather not replace the coupling but I'm aware it maybe inevitable. Any
tips appreciated.

Thanks