Car: 86 Volvo 240 wagon, automatic, RWD.
Problem: Leaking transmission?

I recently had my car towed due to a rusted out spring seat. The tow truck was not a flat bed. I tried to get a flat bed but couldn’t, it’s a long story. Anyway, the guy showed up and began hooking up the front of the car. I told him the car is in park, he nods. He then begins pulling it in close with his hydraulics and the rear wheels on my car begin to squeal. I yell, and he stops. I put it in neutral and from that point on we hear a squeak sound from the rear end. He tells me to start the car, I ask why. “It keeps the transmission warm”. Seems to be a good idea so I do. We begin towing, squeak persists. It’s loud, we can hear it from the cab of the truck. When we get up to about 15mph it stops. We tow it for about 20 miles to my home. I pay him and he leaves. That weekend I fix the spring seat. On my first ride out the transmission makes a loud clunk sound every time I put it in drive. The wife suggests I check the fluid. When I check it, it’s really low. Really. I bring it up to a normal level, the clunk is now gone. Several days later I’m noticing a small puddle under the transmission. I check the fluid again and it’s lower but at an acceptable level. My theory is that I have a slow leak. I’m a newbie to this mechanic stuff and I’ve never dealt with a leaking transmission before. Below are my many questions.

Can towing a car this way damage the transmission in this way?
Is it possible for fluid to leak out this much if the car is up at an angle?
Maybe the squeak isn’t related to the transmission but something else on the rear axle?
Does leaving the car running really help?
What’s the best way to find a leak, if it is a leak?

Thanks in advance.
-SteveC