[plain OM]

I found that the bulbs were dandy fine, but were VERY touchy in the sockets. In other words, they would work fine if the bulb was JUST right in the socket . . . . . Could it be my sockets or just a bad run of bulbs?

I think you're on the right track here. If moving the bulb just a bit makes a difference, there's a bad contact. Check inside the sockets for corrosion on the metal parts, and down at the bottom, check that the contacts (should be two for the combination tail/stop light bulbs) are clean. (It could also be a problem where the wires connect to those two contacts in the base of the socket, but less likely.)

The fact that both new tail/stop light bulbs seem to have the same problem, it sort of points to the bulbs, but if they're the right type, this shouldn't happen. My 07 Owners Manual doesn't indicate the actual bulb model/number, just the Wattage of the two filaments (21/5). However, the original bulbs should have the type number impressed on the metal base.

 

[plain OM]

What number bulbs are they?

I thought the larger, two-filament bulbs used for the tail/stop lights have a round metal base with two small protrusions, the design otherwise being known as a "bayonet" base. When inserted, the protrusions follow either a groove or indentation in the socket wall, and when bottomed out, the bulb is turned a small amount to lock it in place. Perhaps this isn't the type being used, but if it is a bayonet base, it should be turned to lock in otherwise the bulb can work itself back out. (Ref: Bayonet mount - Wikipedia, the free encyclopedia)

 

[plain OM]

Sort of answered my question:

I had a closer look (from the outside) at the tail/stop light bulbs in my 07 rear combination light assembly and they are not bayonet mount; they're a "glass wedge" base. I found a reference to it possibly being #7443, which is a dual filament bulb. Now I understand your reference to the base not being in far enough. I was envisaging the metal base of the traditional bayonet. and it's nothing like that.