[Guerilla]

First off this is a 94 Cadillac Seville SLS with 120k miles on it

This all started yesterday i sent my dad to get my windows tinted and he came by the store im workin at to show me and when he parked we noticed a bit of smoke from under the car, and then we saw something dripping which turned out to be coolant, my dad gets a rag and opens the cap for the coolant and then bam it came out like crazy from under the front passenger side of the car.

I took it to the mechanic across the street and he said that my catalytic converter is overheating (he ran the car and the cat turned red =/ ) so they send me to the muffler shop and the guy says he will fix the cat for me for $140 i was happy as shit and then he pulls out a saw cuts it off from the two sides and welds an aftermarket one on and i drove it home with no problems.

I took the car for a drive and then i noticed the temp was really really high and i was cruising the temp was around 240 (mine never goes that high) so i stop and open the coolant cap and then the same thing happened, all the coolant leaked out from the same spot as before and a guy saw this happening and came and told me that my Coolant Sending Unit is probably fried. He pulls out some tools and says let me check your thermostat and when we started looking the thermostat had no gasket on it and he says that could be the problem and told me to get a new thermostat and gasket and meet him tomorrow and he will fix it for me.

Is the thermostat the problem here or is it something else?
I really need some info on this