Please, Father took into account your transformation. The older models would just change size, the new models store themselves when in your true...er cursed form. Sorry it may be that I'm a clone of Himitsu, or the fact that there's not crescent on your forehead, but I need to keep reminding myself that the talking cat is your true form. As for the grease affecting the collar, you really underestimate father's tech. While such a thing wouldn't be indestructible, it would be waterproof, grease proof, and Greece proof. Don't ask me about that last one, Father includes it in most of his inventions.
I knew I made one already. Pretty certain as long as the attack isn't direct against the collar, the collar has less of a chance of being damaged. Also like liquid attacks electric attacks would fail. As for the matter of your deaths, Cybertronians have long since been familiar with the concept of tangible souls. It's how Rinox was able to rescue Primal, pretty sure the collar returning to you after you die was always a feature.
Then last thing, in the most recent versions, is it matches your fur so it's not visible unless on knows it's there. In older models dad put some kind of charm on it and colored it white. One of the charms being the maximal sigil, another being Himitsu's severed head.