Reading the description of The lesh is Weak talent, i am asking myself, what kind of effect would a Medicae application have on such a character, i am well aware that the rulebook makes no difference there, healing is just healing. I am curious however to see some opinions on this issue, would a diminished effect (or even no effect at all) be justified ? If so, to which extent and how to balance something like that ?

Well perhaps one could say that depending on the level of The Flesh is Weak they have you slowly need to shift to using tech use to heal them? logicly there is less flesh to heal and more machine to upkeep. my two cents.

I would not impose a penalty on a Techmarine for purchasing a talent(s) available via his career path. If you do impose a healing penalty, then at least allow the Techmarine to make a Techuse check to repair whatever damage is left.

Dan.

The most simple way is the dark heresy Mechanicus Implants healing rule.

While the character is healing they are assumed to be repairing themselves.