If the pump quits, just replace the pump. The diaphragm inside the diff can only withstand about 10psi. The ARB pump is probably way too powerful.
If the problem is inside the diff itself (say the diaphragm sprung a leak, like mine did) it's probably the simplest fix short of replacing the diff: get some manual hubs, then pull the diff down and just find something to hold the ring over in place of the diaphragm. Like I said all I needed was 2 or 3 long skinny zip ties, they were the perfect width to hold the engaging ring over forcing the front c/v axles to be engaged full time.
Once the you have the front diff down out of the car and opened up the actual "repair" takes probably a minute or two, then you bolt it all back together. You just need a way to hold the diff "activated" while you install the zip ties, best with an air supply and a gentle hand - you want just enough air pressure to keep it fully engaged, you don't want to completely blow-out the diaphragm before you're done!
You can move the engaging ring over with your fingers, it's that light. Seriously this is so simple a fix, if your stock air diff crapped out and the light's flashing and you just want to get 4wd back up and running this pretty much all you need. I mean heck you could even forgo the manual hubs but that means the front driveline would be spinning 100% of the time, even in 2wd, and could cause other problems down the road (No way to disengage front driveline from front wheels). You don't need to run to a machine shop or get something made out of heavy plastic - it's not necessary. Not from my experience so far, anyways.
THAT SAID, my GV is a v6 manual, which means I have the stronger steel case, not the aluminum one. And I'm running stock-diameter tires. The last snowstorm I was out doing parking lot donuts and it did not clunk or bang AT ALL. The only clunk I ever get is from the transfer case - sometimes - when it's disengaging on a hard surface.
Of course if you want to use a front diff failure as an excuse to upgrade your front and rear diffs to higher ratios and make a big tools-and-parts-all-over-the-garage-floor project, by all means be my guest. Obviously you must know what you're doing and what you want. In my case my GV is my daily driver and I don't have a backup car so I had to just fix it quick.
It has not been a full year yet - that's coming March '09. I'm still driving it with the hubs locked full time over the winter - haven't unlocked them since I installed my winter tires! Still slips in and out of 4wd really easy. It really is too bad that I couldn't take pictures or video of how the zip ties are in there, because I'd like to make-up a how-to article.
James