alright heres my problem. i got this 91 dx with a ls motor in it, and the guy tells me to only use synthetic oil in it. i thought that was a little weird, its an old motor, but it hasnt leaked any oil so i havent put any in, and i need to do an oil change, and im wondering if i put synthetic or not. i heard that once u put synthetic in, you cant go back to the regular stuff. is there a way to tell if the oil is really synthetic. the only reason i ask is because the guy lied about a lot of stuff to make it seem better, so im thinking maybe he lied about this. anyways so should i just put some synthetic oil in it? im afraid its not synthetic and when i do put it in my gaskets are all gonna leak n sheit. any help pleases