Quick Question

I have an autolite,
This thing is weird, yesterday after I'd start it up it would be at 600, after a press of the gas it would rest at 850. Then i went for a drive at night so i couldn't see the gauge. Today, after checking the carb I turned it on, it started off at 600 and stayed there, I scratched my head, pressed the gas it came bak to 600 I said ok... Put it in drive and it went down to 500ish. Ok, I put it park again and it went to 650. I let it run for 10 minutes, tried it again, put it in drive, this time it went all the way down to 200 and in park it stayed at 450. I moved the car up (its on a slope in the drive way) and put it back in park and now its at 550 in park.
I'm confused.

(The day I took the first readings with the tach, the car hadn't been moved for 3-4 days)

I took it for a drive, checking the gauge at every light, and again it varied from 450 - 850 rpm. It shook sometimes and didn't at other times.

The car does leak engine and transmission fluid according to the mechanic. I knew it leaked but he said it was transmission fluid and oil, he said that the main seal between the engine and tranny is worn out. He said don't worry about it cause if he does the work it will cost a lot in service. My dad says that when he had to do it on his firebird many years ago cost was 1600, they both said to just put a plastic oil tray under it when its parked and pull it out when ur about to go. (I haven't tuned it myself yet)


Edit: the oil pressure gauge stays at 55 psi and when I accelerate it is at 60ish, if that helps any

Does anyone know how to get rid of oil stains from concrete, I made a boo boo and my mom flipped out.

thx guys i'll try it today

as for the tuning issues, after i've been driving it on a daily basis for the last 3 days the rpm has been fine, always in the correct range, 650 idle in park 450-500 idle in drive