"The points of friction I understand and have suspected, especially since the notes with that narrow, flat bar screwed down across them are the ones that go out; the tenor and bass strings never go out, and they don't have those extra friction points."
And there you go! More information - that the problem notes are only in the area with the pressure bar.
In all fairness, that is not more information, that is literally how all pianos function. Unless we are talking about a humidity issue, all pianos are more stable in the bass and tenor. The pressure bar may be out of range, and raising it could help, but you can test it before you go through the trouble. Put a half round between the bridge pins of a unison and observe how the tuning functions. The pressure bar won't be any obstacle in the slightest. If you change the pressure bar height, you have to lower the tension. The lowering of the tension results in a reset of the tuning system. Obviously, the tuning has to start anew. If you are not aware of this, then one would assume, naturally, that the adjustment of the pressure bar solved the problem. That's not the cause. The pressure bar may slightly contribute to the issue, but it won't be the main cause. Since the majority of techs never take time to feel what the system feels like without the bridge pins in the scenario, they make a lot of false assumptions about how much friction is present in these various bearing points.
While I posted the link to the more commonly available CLP, the counter bearing lubricant from Jon Page that was also referenced is really the way to go for this specific situation. Hard to imagine any danger using it in this area of the piano in a controlled manner.
It is not hard to imagine the dangers of using a lubricant on a vibrating string. I am glad that OP has decided not to do this.
I tested this unfortunate procedure on a piano that was being trashed a long time ago. It doesn't matter where you the lubricate, it will migrate everywhere. Mario Igrec statement of "rubbing the strings with the lubricant felt wedge, against the bridge pins, but without touching the bridge," was ridiculous. Within seconds of playing, whatever is being used, will be on the bridge, on the back side of the bridge, in the hammers, on the action, on the soundboard, everywhere. In fact, I believe both Yamaha and Kawai in the USA had problems with a technician putting this kind of things on their pianos. It was a huge problem that messed up a lot of pianos. I believe lawsuits were in the works, but I never hear what the end result was. In any event, if piano manufactures don't lube their strings, and don't recommend the procedure, then there is a reason why.
Just because something seems to work, doesn't mean that it should be done. If it is a junk piano, the lub stuff may give it a few more years perhaps. But, it is not something that should be talked about as if it were a standard approach. Again, this is a palliative care measure. It is not something that should be openly promoted.