Older?? how old?? is it still in warranty,? What type of media. Try different media, and try it in a different computer if you have one available. It could be that you are just wearing out the burning, God knows I have went through about 8 different burners,
one being a mitsumi(4804te same as yours). Of course I am slighly hellish on the burners I have, they have to be able to burn a LOT of cds!!(my mitsumi burnt 350 in 3months),
I guess I need a industrial strength burner. !!