Part code confusion for Ultrabay slim DVD burner

[martinjco]

I'm off to buy a DVD burner for my T60 (8741-4GG) - the Lenovo site lists part code 41N5643 as the part compatible with my model, however when searching for parts available from any of the dealers, it appears to be part # 40Y8623.

The specs look the same to me.. are these the same drives? Is the 41xxxx just a later revision and I should wait for it to be more widely available, or should I just go ahead and get the 40xxxx?