Actually, I do (our entire troupe does). It's arguably somewhat subtle and occasionally difficult to adjudicate; more importantly, it's rarely an issue because most of the times one just uses T:Ind rather than T:Part. But the difference is there, and the key is whether the "part" you are targeting acts as a single individual (albeit part of something larger) or as a group. Consider Pit of the gaping Earth, or a similar "I dig a hole under a victim's feet" spell, where the target is Part for obvious reasons. Now consider a version where, instead of a single pit, a magus can create a dozen, each affecting (the ground under) a different victim. Would you leave T:Part, or make it T:Group? We'd make it T:Group, without doubt. It seems to me you'd make it T:Part.
No. The keyhole suggests the presence of the mechanism, just like a coffin suggests the presence of a corpse, but you can't actually perceive it the way you can perceive a fetus in a belly, or a man under a blanket. For example, you can't quite tell how deep or large the mechanism is. I realize the boundary is fuzzy, but there must be a boundary, or otherwise you'd be able to light a specific, unseen fireplace in a faraway castle (which we do not allow barring Arcane Connections or other workarounds; would you?)
I may not have been clear, but I meant:
- In an ingot of electrum (an alloy of gold and silver), you can target the gold with T:Part.
- If there's a small ingot of gold, encased in a larger ingot of silver, you can't target the gold with T:Part (and/or at R:Touch).
"Remove water from a watery body" is akin to 1. "Act upon a hidden mechanism inside a box" is akin to 2.
Obviously, we are talking about T:Part, not T:Room etc.
Can you destroy the inner lining of a closed boxed with T:Part? And at R:Touch?
Our troupe disallows it, and we do not think it's a house rule. Find me a similar example (but one that's really similar, not those you've brought to the table so far), and I'll be happy to change my view.
That seems rather different, but I am not quite familiar with the spell you are referencing, so I cannot comment further.
That said, it seems to me that:
a) we might be in agreement that to open the lock, you can target the Individual lock (using the guideline about "controlling it in a natural way") and you do not need to target a Part of the lock;
b) we disagree on how "hidden" a targetable part might be, which is rather off-topic for this thread;
c) we disagree on how a "group of Parts from the same Ind" should be treated, always as Part (your view) or sometimes as Group (mine) - again, rather off-topic;
d) while there may be some examples that hint one way or another, there's no clear-cut ruling in RAW about b) or c), so we are unlikely to resolve the issues further by discussing them; but if we want to discuss them further, perhaps with input from others, I'd suggest opening a new thread.