about the fluids: get them checked. the clear amber fluid may be brake fluid. check the reservoir and see if the colors match up. the dirty oil color may actually be oil, possibly an RMS leak or the oil filler tube is cracked. maybe the people who changed the oil last time did not put the crush ring on or the oil filter canister is not on correctly.
as far as the mid-grade gas goes i don't think a few miles of it would cause the light to come on. it could be possible that it was only filled with regular instead of premium while it sat on the lot and now it's complaining. if it's not running badly i wouldn't worry too much about it but you might want to get the CEL code checked anyway - most auto parts stores are more than happy to get the code from the computer for you. you can then search on the internet for what it means. after getting the code you can disconnect the battery and it may reset itself (make sure you have the radio code - i am guessing that since there was no manual, there is no radio code). otherwise look into getting a durametric or something that can clear the codes for you. no need to pay $$$ to a dealer unless you just want to.
is it a manual or tip?