2001 Sienna went to get an oil change. Oil Plug loose, leak all the oil ...what now?

[2k1Sienna]

Just bought a 2001 Sienna LE minivan used from a private party. I figure let me get a oil change and stuff so I know when will I have to do the next oil change. Went to one of those mom and pop mechanics and they changed my oil. I drove out and about 5 blocks, my oil pressure light starting to flash and lit. I look underneath my Sienna and oil was dripping out. I quickly turned around and went back and they tighten the nut and refill about another 4 quarts of oil in it and said everything will be ok. So I drove off. Now when I am driving I hear engine noise (I think its lifters or valves) when in Drive or Reverse. When its in Park or Neutral its quiet. What should I do? Will a bottle of Slick 50 fix this or am I in DEEP TROUBLE. I had the car for less then a week. Its a 2001 Toyota Sienna LE with only 56,000 miles and I just paid $12,000 for it. Can anyone tell me what are my options?

[drunken_panda]

Go back and complain to the oil change place. They caused the problem, they should fix it. 4qts is a lot to be low. When the pressure light comes on, that means bad things happening, you shouldn't have driven back with it on.

[Cyorke]

Take it back. they screwed it up. The engine only holds 5 quarts of oil or so. That being said there was pretty much none left after the oil leaked out.

[lsac]

A plastic washer was left behind. I did have problem once after DIY. A quick hand won't lose too much oil. Half qt is enough.