W220 Trunk Assist not opening or closing

[speace]

My 2002 S500 W220 suddenly refused to "pop" the trunk.

I dug out the physical key and was able to open the trunk to get the groceries out, but it also refuses to assist when closing the trunk.

There are plenty of posts here about how this works on the older chassis, but I don't see much on the newer cars about this.

I hear a subdued "thunk" when I hit the release button, but nothing on the mechanism appears to even be trying to move to open the latch.

I'm not sure where to start on this to see if it is the release mechanism, or a problem with the vacuum pump...