Is your drive a real 832S or is it crossflashed? Any reason why you are not using the latest firmware VS0E or CG3E?
MKM001 is probably one of the better DL discs but they are quite variable and this is a typical result with some of them. Some that I have, have little visible spots that cause high errors at the location on the disc where the spots are.
Verbatim does have a replacement guarantee and I have heard of people getiing replacments on burned discs that failed. Seems like an big hassle though.
Maybe you could try another one with VS0E or CG3E. Your call...