may be the action stack is slightly bowed, pushing a little the lift rod out of alignment.
I never have seen much tolerance problems on the lift rod, and the pivots are tolerant, they are screwed in place in regard of the rod.
Did the tuners test separately the dampers (by hand) and the rod ?
It may be a 1 hour job to dismount all necessary parts to have access to the rod, correct any cracking problem and replace.
Listening, it sound like a spring that have a non smooth path at some point, but indeed if it was traced to be within the damper rod pivots, I do not understand why it is not cured yet.
You can unscrew the 3-4 bolts that secure the stack, take out if necessary the left pedal vertical rod, and incline the action so you can test separately the dampers and the rod. Then push on the rod while pushing on the dampers with a stick or by hand (so you may locate more precisely where the crack is coming from )
push on the wooden blades, not on the felts.
Often, the action inclined ois sort of secured, you do not need to secure it to the bolts in the frame, but it can be done with an electrical wire so you do not need to hold the action while testing (or wooden block(s) between the keys and the hammer rest rail).
I am sorry that if the noise comes from the rod you need a technician. If the return spring produce the crack it may be easy, and easy to test, put a finger on the spring while moving the rod, a strong crack can be perceived that way (or diseappear, sign that the blade leathere need a lube)
STrong lubes are used for strong friction, while a greasy leather will crack, eventually (I do not trust Teflon for hard friction nor for leather) Graphite (or even pencil) have its use , of course not in some places (not on buckskin leather for instance)
Talcum is also efficient , need to be mixed with a little tallow and bees wax so it is not too greasy.
If a leather produce cracks it is often a surface defect it need to be cleaned/surfaced before lubrication (almost "dry lube")
Cracks are often audible when springs are effectively pushing on the rod, be it damper springs or return springs, and the rod does not pivots cleanly for some reason. SO with the rod alone (maximum dampers pushed with a long stick) you may just feel that it does not move freely, but you will hear nothing.
BTW lubing the keybed of grands with graphite is for idiots ! it does not work, and the keyframe is more efficiently lightly sanded so to raise the fiber, a little talcum used while sanding.
NOthing more. I used Teflon spray but stopped because of fumes going all around. I prefer not to have teflon particules anywhere near the piano, in case I have to glue back something someday. (
BTW it is still a guarantee job, as it have not been fixed before, in my opinion.