If you really want to clean her up throw some Mobil Delvac 1 in. Its a diesel full synth 5w40 and can be picked up for under $60 ($50 here in Adelaide)
Don't let diesel scare you, its perfectly fine in a petrol engine and meets the API SL specification for gasoline engines, mobil state so them selves.
http://www.mobil.com/USA-English/Lubes/PDS...vac_1_5W-40.asp
OR.. Even better, throw Motul 300v through it, nothing cleans like an ester based oil.
Bob is the Oil Guy