Opinions on how much DIY electrical is too much in a 70s house?

I had a similar scare with an old Zinsco panel in my last house. Those 70s setups are notorious for bus bar corrosion that you can't always see untill you pull every breaker. Even if your Fluke is reading 120v now, the fact that your lights are still flickering suggests you have a high-resistance connection somewhere. If the insulation is already crumbling, you're looking at a fire hazard, not just a nuisance. The moment I see significant pitting on the bus or heat damage on the main lugs, I back off. Working in a crowded, unlabeled box where you can't even tell wich wire goes to which circuit is how people get hung up. I tried chasing a floating neutral for three days before realizing the main lug was literally vibrating under load.

For me, the line is drawn when the hardware itself is failing. If you have to fight the panel just to get a clean contact, it is time for a service upgrade. It's much cheaper to pay a licensed sparky to swap in a clean Square D or Eaton load center than to wait for that old gear to arc out behind the dead front.

Everyone jumps to the panel being a death trap becuase it's old, but I’ve seen plenty of 70s Square D or I-Line setups that look like a rat's nest but still carry a load perfectly fine. If your meter is holding steady at 120v under load now, you might be chasing a ghost in the service entrance. I'd start by checking the neutral wire right at the kitchen outlet box. Those old back-stabbed receptacles lose thier spring tension over forty years and cause exactly the kind of flickering you’re seeing when the microwave draws high current. Before you commit to a full panel swap, try moving the microwave to a diffrent circuit on a different phase with an extension cord. If the flicker stops, you know it’s just that one branch circuit rather than a bus bar issue. I once spent three days troubleshooting a "corroded" panel only to find a loose wire nut in a junction box tucked behind the drywall. Sometimes a $5 Cooper outlet is all you need to stop the flickering, regardless of how rough the main insulation looks.

Look, if you're seeing flickering but your meter says 120v, your meter's probly just too slow to catch the dip. I've dealt with this before and it's ussually a loose lug. Since you mentioned that insulation's toast, I wouldn't touch it. Once the wires start crumbling in your hands, you're one slip away from a big flash. I'd call a pro just 'cause you don't wanna be the one holding the screwdriver when a brittle wire snaps off. It's a total pain when you can't even move stuff around without it falling apart.

I had the same flickering and it wasn't the panel at all. I wasted a weekend tightening every lug in the house just to find out it was the overhead service line from the street. One of the crimps at the weatherhead was loose and arching whenever the wind blew. If you’ve checked the panel and it’s staying at 120v, take a look at where the wires come off the pole. I called the utility company, they came out for free, and fixed thier side in ten minutes. Saved me the cost of a panel swap I didn't acutally need.

Back before everyone had these fancy digital meters that lie when the battery gets low, we used a Wiggy. A solenoid tester doesn't give you ghost readings. If you're seeing 120v now but the microwave is still acting up, put a heavy load on that circuit—like a space heater—and watch the meter. If one leg drops and the other climbs, you've defintely got a loose neutral. I’ve seen plenty of 70s cans where the main bonding screw is just a ball of rust. If that insulation is truly crumbling, don't even try to tighten anything. You'll just crack the jacket and end up with a face full of sparks. Time for a new load center.