That was the sort of conclusion I was dreading. I do have a perfectly good 2465 (no suffix) with what I believe is the same CRT. It pains me though to pull a CRT out of an otherwise healthy scope just to prove that the subject unit has a weak CRT. I suppose it's that or roll the dice and buy a CRT off of EBay. There's a seller from Israel offering 154-0850-01 CRTs for $67, shipping included. "Very Good Working Condition." I'll admit to being a little apprehensive about buying parts from overseas.
One other thought: In the good old CRT television days, (were those the good old days?) one could often perk up a sagging CRT by bumping up the filament voltage on the heater. Sounds like something of a fool's errand for a tek scope of this sort, and more effort than it could possibly be worth, but I would be interested in knowing if anyone's ever given it a try.