Are newer Tele jacks different than old ones?
When I plug a cable in my 68, you can feel it pop in reliably. You have to make sure the jack is all tight and everything, but other than that, no problems. Maybe I got lucky.
They used Switchcraft brand jacks in that era. Now that's not a guarantee, particularly on the imported guitars.
I guess the spec on them has probably drifted a little with that.
Side note - as far as 90 degree cables go, I like the jacks that are completely non recessed and pop out on guitars like a Tele, but they aren't a clean replacement since they require extra screws.
Switchcraft spec on their #11 jack is remarkably pretty much the same, as far as I can tell.
It's that many guitar makers, particularly on their more affordable (read: imported) lines, often use other vendors for the jack. This is where we invariably run into problems, as these are almost always inferior in quality.
Bearing in mind that the tip connection of the jack is, in addition to an electrical contact, basically a quarter-elliptic leaf spring. And this spring's compliance, or resistance to compression, has a direct effect on the jack's ability to perform its job of making an electrical contact. And the spring's durability has a direct effect on its ability to perform this job reliably over thousands and thousands of compression cycles.
Lots of the less expensive jacks are basically flimsier springs, and over time (like any cheap or flimsy spring) they get "sprung" and don't make as effective a contact.
You can bend it back, over and over again until metal fatigue inevitably causes it to eventually break. But that's kind of like airing up a tire with a slow leak-- it will remediate the symptom for a time, but it does not address the fundamental problem, which in this case is a spring that's too compliant.