There were a number of minor failures of Design 1/2:

1. Incorrectly curing the resin part - Formlabs have fairly simple, but precise, instructions on how to post-process the resin part once printed. On some test parts I skimped on some of these steps and the result was a weak part which broke during testing.
2. Dimension accuracy - The Form2's dimensional accuracy is extremely good and the parts design has very tight tolerances. If I failed to clean the excess resin well after printing, even a small layer left during curing could reduce the size of the filament channel enough to make the part unusable.
3. Heater block threading - The thread on the heater block is standard M6. Originally I printed an M6 thread on the heatsink but found this too tight a fit (possibly, but so tight the thread could sheer). Reducing this to, essentially, M5.9 made for a better fit.
4. Heater block clearance - With the heatsink screwed into the heater block, the fan was originally placed very close (almost touching) the heater block. A little extra space was added at the base of the block to give the fan a little more clearance.