Net build lash engines (non adjustable valvetrain) have several different length pushrods available. Was the correct length one supplied and installed? As a retired engine builder, I have seen the wrong parts supplied often, not just with Buicks, but with other brands too. There are several different versions of "knockoff" springs out there too. Different length and pressures too, but unless inspected next to another, they may look the same.
If you are in there to replace a "bad" part, find the cause for the repeated failure, don't just replace the part, or you may be doing the job again. You are at the mercy (knowlege, or lack of it) of everyone that worked on it first. You have to remove the rocker shaft, so why not dissemble it and look for more problems. Same with pushrods, see if they are the same length, and compare that to the correct length, really look at the springs too!
If you didn't find what caused the (repeated) problem, you are doomed to repeat it. A lifter going bad may occasionally "pump up", that too can bend a pushrod if the retainer to seal distance is short.
My point is; don't just fix the symptom, find the cause.
TIMINATOR