Some years back, I ran across this YouTube video of a gentleman who had an older type Milwaukee 6390 7-1/4" saw that quit running.
He disconnected the Trigger Switch and carefully worked the plastic halves apart. He had a spring handy to replace the one in there, but he demonstrated it was still good. He could see corrosion on the contacts and he used successive grades of sandpaper to work em to a polished surface. He got that switch back into  the saw and it ran again.
That video sort of inspired me. It was so simple and straight forward. I watched again later and then went back to see any other videos he had, but it was gone. For good it turns out.

I worked at restoring another one of those big drills I like so much. I got it all done and pulled the trigger. And nothing happened.
The multimeter indicated the switch was at fault. The first picture shows the Trigger Switch as I'd initially found it. The next shows as it now looked and it's certainly an improvement. I wondered why it picked now to quit.
On the right, the white neutral wire is directly connected to one of the motor wires, so that's no concern.I looked inside and it seemed things  had been bad enough, but when I cleaned the trigger and springs with kerosene , it washed some sludge inside onto the contacts.
Third picture shows the inner workings. I took things apart, used a diamond file and finished off with 600 sandpaper.  The wires connect to these thin copper strips; two sheets each. The red hot wire is connected down on the far left. Adjacent to it but topside, the other motor wire is connected. 
Squeezing the trigger causes this copper ball to make contact between these two sets of copper strips.
Fourth picture is when I tested things. I actually had that big drill laying on some plywood and when I pulled the trigger, it jumped enough to shake me off.

Seems you can significantly extend the life of a Trigger Switch. This switch of mine is pret'near 70 years old. And who's to say it can't last another 70, owing to its sort of indestructible nature and continued loving care.
I just checked the state of things concerning the Milwaukee 6390 switch. Seems the older model types; all but the newest of the five, are "No Longer Available".

Anyone with their own switch story, feel free to throw in.

Model Ichi Ni, funny you mention about the insides of that switch. In an old Rockwell 1/2 " drill from the late 50s the switch quit after it got run over by a log truck in the mud.  Well, my uncle was about to toss it, mostly out if frustration, but I took it apart to have a look see. Turns out mud had jammed up in there and destroyed one of the two metal connections you mention.  I took a penny and mashed it flat with a peening hammer, which took a while as you'd imagine. But it worked. Flattened it then pounded it out into a strip, sanded and found it down to size, and stuck it in there with this mix-up epoxy we had back then. I think you can still get it in little tubes.  No way that would work, right?  But somehow it did!
I believe eventually they put a new switch in it though I'm not sure. Regardless, my flattened penny lasted through the rest of that particular job and a long time thereafter! Man, that was a lot of years ago.

Omeomai, that's one Hell of a story.
The truck running over it in mud, basically destroyed the Trigger Switch. But you brought it back to life.
I had my own situation some years back. Doesn't begin to stack up next to your skill and the amazing way you improvised.
The on and sudden off, intermittent behavior of my Milwaukee 6523 Sawzall would have led most anyone to believe the Switch (25) was going bad. I ordered a new one soon as it quit running all together.
At first, the new Switch seemed to fix things, but real quick it was the same story.
Then I remembered how this one time way before the trouble, I was using the darn thing and the Orbit Shift Lever (39) somehow got shoved from off to full throttle. The Sawzall bucked rodeo hard a bunch of times and then I lost my grip. It fell to the ground from a considerable height. Better it than me I reckon.
Armed with recovered memory, I now figured both switches were blameless. I disconnected and removed every wire and part from the Motor Housing (38) on back. Then I secured it all into place again. Took a good length of time. Things involved with that handle rotating feature (22); brushes too (23), were tricky.
What was shaken loose or whatever, remains a mystery. Be that as it may, without fail the Switch has since turned on and remained so as required.