Why is there is used engine oil inside as well as out on the radiator header tank on an s reg v6 vectra.?

the car has just been given to me and is currently a non runner.it has been stood for about a year. its too good to scrap with super bodywork and 16 inch sport alloys. even the spare wheel has never seen daylight. can anyone give sensible advice before i spend any money on it. thanks.