Don't know if this is helpful or not. Here is the link to the optical drive catalog for Liteon PC drives. http://www.liteonit.com/ODD/English/e_product/e_dvd%20rw.asp
From what I have read in the past, in this forum, the DDW-813s is essentially the same as the LDW-851S. The DDw-451S is essentially the same as the LDW-451S. There are no indications in the specifications that separate lasers are used. This does not mean that they aren't, just that they are not indicated.
Several forum members have tried replacing the DDW drives with PC drives with mixed success. Here is a link to a thread by nickkk that was pretty detailed. http://club.cdfreaks.com/showthread.php?t=125214 The conclusion being that it will work for most everything but reading encrypted commercial DVDs. I bring this up as this may be a potential low cost solution for others that may have garygad's problem but are beyond warranty.
I have sent the following e-mail to Liteon Tech Support and will post back if I receive an answer to my questions.
I have[I] read in some forums that the LVW5005 comes equipped with two different drives, depending on date of manufacture.
Older models have the DDW-451S
Newer models have the DDW-813S
This leaves me with some questions.
1). What are the differences in the two drives?
2). In your ODD catalog you have LDW-451S and LDW-851S for PC application. Can these be used as replacement drives if the DDW version fails?
3). I have read that the CD writing and DVD writing feature of the DDW drives have separate lasers, is this true?