You might try cleaning the laser. After two years, it might just be crap settling on it.
I have used my Philips DVDR75 aggressively for about two years without any problems at all until a few months ago - probably burned at least 500 discs with many different brands of media. A while back I started seeing errors like you described, so I thought the recorder was dieing. I, too, discovered that +RWs would still record, so I just started using them and dubbing all of the discs on one of my computers to the blank +Rs I had left. Oddly enough, I began having more and more errors on these copies too. Sometimes the copy wouldn’t finish, but many that did wouldn’t play correctly on any of my players, especially toward the end of the recording. I was also noticing that the errors in recording that I saw on both the Philips and the computers seems to mostly happen toward the outside edge of the disc. If I wouldn’t try to fill them all the way up, many more recording sessions worked fine.
It turns out that the recorder wasn’t going bad, it was the MEDIA! I had purchased several hundred blank DVD+Rs on sale sometime last year, various brands, and the errors were happening on all of them. And all of these were down to the bottom 1/4 or so blanks on the spindles. I had been using them all randomly, as some were sitting in by my computer, some by the TV, etc. I had originally opened each package and started using them to verify the compatibility with my recorder, so I knew that all of them had been working fine (BTW - every brand I have ever tried, most on sale and not major names, has worked perfectly with this machine). Now the problems were happening with all of them, and not just in the Philips DVDR75, but also in three burners in two different computers.
As soon as I bought new media, the problems went away! It seems like blank DVD+R media have very definite shelf lives, and it doesn’t matter much if they are stored in the dark or out in the open. True, I was having more errors on the disks that had been sitting on the open shelf, but even ones that had been in a dark cabinet were causing problems. I don’t know for sure how old they were, but most of them were bought around the same time, probably 12 - 18 months ago, and they all seemed to start having problems around the same time. And I had 5 or 6 DVD+R blanks that I had only partially recorded and left sitting in folders waiting to find just the right thing to add to them - every one of those that had been sitting for close to a year went bad when I added something else and tried to finalize the disc.
Since I finally figured out it was the media, I have burned through about 95 more blanks without any problems, not even a single error. And these are bulk no-name blanks bought from Comp-USA. I know you said you bought new media, but I thought I’d share my experience with y’all anyway - hope it helps someone! Good luck,