Has anyone opened up and cleaned sticking analog gauges? I read somewhere that overtime small magnetic particles get into the mechanism causing this. Can one open them up without destroying them? Getting tired of tapping them to return to zero.

The needle of my Brick's tachometer was stuck on a barely visible distortion of the faceplate's veneer. I opened the case, gently removed the needle by capturing it between the tines of a fork to lift it off its axle and attempted to flatten the veneer. That worked temporarily but I eventually replaced the plate with one from a used cluster when distortion arose at a different point on the plate. All's well these days.

Maybe my title caused confusion. These are the gauges I would like to open up. Is there a technique to getting them apart or am I SOL?

In 50+ years of working on bikes and cars I have never heard of "magnetic particles" getting into a gauge. 

I am pretty sure you are SOL, I can't ever recall seeing a gauge that could be opened and resealed that it would keep water out and still work. 

My advice is to just get another pair of cheap gauges and replace the old ones.

I do exactly what .75 suggested.

Not repairable. The back of the glass (actually, plastic, but we won't argue about that ) has an anti-fog layer on it. You can sometimes see it peeling off the OEM gauges because it appears to be dirt on the front of the glass, but of course, doesn't rub off when you try to clean it.

Both of those will cost you about 30 bucks each as a no-name and about 70 bucks each as a VDO, which is probably a no-name with VDO printed on it.

Cynical? Who, me?

You can get the bezel off but it's as fiddly as hell and if you're not familiar with doing it, it's very easy to split the bezel and render it useless. I now have a small electrician's screwdriver ground to a specific shape for doing that particular job, but I screwed up a few 80mm speedos and tachos in my early days of learning how to do it and the 80mm ones are a lot easier to dismantle than the 52mm auxiliary-type gauges. They are resealable but that too is as fiddly as hell; they need a lot of downward pressure to hold the bezel and glass in place when very carefully refolding the bezel edge. 80mm gauges are easy to do in that respect; for the 52mm auxiliary-type gauges I finish up by running a bead of impact adhesive around the folded edge, recognising that I'm never going to get that gauge apart again.