Most all the plastic in the dash and trim are an ABS plastic. Ozone and heat are their enemy, they get brittle with age. For the cluster repair I've used Plastruct to glue the broken parts back together. Another glue is Tamiya, both cements are used for assembling models and can be found at a hobby shop. If you can find a hobby shop today. Both are also available on Ebay.
For the screw studs that seem to just fall apart I've cemented them back together with Plastruct. Then with a fine mess screen material cut to size used epozy to wrap the studs to make them whole again.
Another thing, never think that a little bit of any lube on the screw threads will help prevent the cracking of the studs when the screws are installed. The ABS plastic studs that are cracking will absorb the oil and totally ruin the plastic studs. Reinstall dry and carefully tighten, don't over tighten. Been there, done that.
The headlight switch bracket is plastic and is always broken at the attachment points. Mike's Monte sells a steel bracket to replace the plastic one. Also there are two different brackets, year depend.
For the printed circuit gauge connection the metal clips in the PC lose contact to the PC. This is the main cause of erratic gauges. They can be carefully removed, tabs rebent to increase tension on the PC. I ground the tips of a thin pair of slip joint pliers as tool to be able to remove the clips, bend the tabs and reinstall the clips. My gas gauge was erratic for several years. A better connection of the clips to the PC fixed that, permanently.
All four of the small gauges are silicone damped internally. Over age that tiny bit of silicone will get displaced and the gauges will not be dampened, the needles will jump around. My volt gauge would dance to the turn signal blinking. Only a new gauge will fix that problem. If you can easily make the needle on the gauge move with just a very light touch the dampening is probably gone. There should be a little resistance to touch.
Where the cluster PC plugs into the dash, clean the copper with a good pencil eraser, wipe them clean with a rag and contact or a like cleaner.
Depending on the condition on the PC sometimes the wise thing is to be a repop. The locations of the bulbs as you mentioned can crack the plastic. Again heat the enemy. The higher wattage miniature bulb upgrade produces more heat. LED upgrade, much less heat. Just something else to spend time and money on when the cluster is apart.
The clusters in these cars were good for many years, unfortunate time, ozone, heat, design have caught up and when you take one apart you open that can of worms.
The reliability problems on the new digital dash seem to be much better today, 15 years ago, NOT. Today they are more versatile, probably more accurate, differently better illumination The cost and install effort of digital, verses maintaining the old stock cluster, to each his own.
I pulled most every gauge cluster I ran across in the U-Pull back in the day when Gs were plentiful. There's a half dozen in a box on the mezz, most in need of lots of repair work, and paint. They were collected to maintain the one in the 86, and modify it.
WAY to much time in the cluster in the car, to many upgrades to go digital now.