To buy or not to buy?

Well I have a Sony Dru-510a and its not burn my Ritek G04 DVD-R@ 4x only 2x....Well I did suspect the drive cuz I was getting alot of coasters...But I was able to burn a DVD+R E-gear @ 4x..
So I used my friends 510a new and It didn't burn my Ritek G04 @4x only 2x..Then I used his PC and same thang..!!!

UPgraded to SP2, re-flashed burner,change from 40pin IDE cable to 80pin IDE cable..Same thing...

So the thing is I know that my burner is mest up, and I want to get another one maybe a 16x dual layer burner not Sony NEC maybe..So what is the chanceses that the Media is not compatible with this drive but will work with newer drives?Cuz I don't want to buy a burner and still only get 2x out of it....

So i leave it to you guys what are ur experience with this type of problem and maybe this drive...