[BrianG]

It's not just the heatsink, but the thermal pads Quark uses to secure the PCB to the case. Not only is it not the best thermal conductor, but it sometimes "lets go" and the FETs don't even touch the case anymore. There is a mod that removes these pads and uses thermal adhesive instead, but that voids the warranty and need to create a new spacer slab. Just search around and you'll eventually see the mod details.

Once the mod is done though, it helps a TON. I ran a 125B in my old Revo and still in my Hyper8 buggy and they worked great. They are VERY smooth even at really slow speeds. I still think they are smoother than the MM or MMM even with the newer software.