I have a Lite-On 5005XA (5101-1) that started the dreaded invalid disk error a while ago.
This is bad for a number of reasons. I record cable programs for a number of disabled vets who do not get cable (fixed income) and the loss of this would be a big set back for them.
The short version is that after about 12 coasters I came online and found all the recommendations to replace the drive after you did all the recommended things first (clean the drive, update the firmware). I went so far as to find a place to get the 160 drives at a reasonable price (newegg.com).
I must have at least one brain cell left because this morning I decided that since I have to take the unit apart to fix it, I should do it now to confirm the drive I have in the 5005XA.
It was a DDW-415.
Having never heard of this drive I did a search and came upon a fellow (jaybird74) on this site with a great walkthrough of cleaning the 451. Mine was not as bad as his but I was able to do finally prepare a disk for recording, and the picture quality improved.
Just wanted to pass this on. Also, if you have a heat problem with the unit, I placed some wooden spacers under the legs and gave the unit about an extra inch of airflow. Sometimes low tech is the answer.