I'm a bit surprised that CitiBear didn't post anything in response, may he's on vacation. Look for his posts in the last 2-3 months, I think there were some discussions about Pioneers recorders.
Otherwise, you're are out of luck. DiY Pio dvd drive replacement is out of question. So if you need to save what you have on the HDD it's either play it and record it onto another dvd recorder in real time or $400 to Pio service.
You can still use your 550 for recording to the HDD with the limitation as above.
If you want a replacement Pio it is only from a second hand market. In Canada you can find a nice used 560 or 660 for a reasonable price, check it around out and decide.