As I said in my first reply to this thread, I've found that 3-in-1 multipurpose oil or silicone grease work well. WD-40 is not a lubricant, and won't last long at all. White lithium grease is common but dries up after just a few months.

As for the upper read/write head and its corresponding spring - I also learned about this the hard way, rendering two Sony SuperDrive mechanisms useless. xx(