Heater O rings etc advice

Water in the RH footwell, just checked and the inevitable heater o rings are leaking. I've changed blend motor before so I will use the shortcut method because my downward ducting is already cut through. reading the threads the biggest problem is likely to be loosening the screw of the o ring retaining plate. Is it pozidrive or philips? Seems best to replace this with a hex or allen head. Does anyone know the thread and length so I can get it before I start please?

Also I want to lubricate the blend motor plastic machanisms because they seemed a bit sticky when I changed them - what's the best to do this - I have been told PTFE spray - would others recommend this or what else? Thanks chaps