Replaced all the cam followers w\ new improved FoMoCo 3L3Z-6564-A cam followers due to finding 1 broken when checking VCT solenoid screens for restrictions. Never heard it break (1 of the intake valve followers on #7 cylinder) or picked it up w\ a mechanics stethoscope....got lucky as the rest was undamaged....cam lobe was like new so broke stuff never hit it, valve spring\stem was undamaged as well as lash adjuster. Follower failure looks like fatigue related (they had 153,000 + mi on them) as there was no evidence of anything rubbing on something prior failure. Something for us high mileage car folks to consider changing out while the getting is good (if you haven't already)…………. PS--(2-12-20)--From my experience w\ this I will also suggest to pull the valve covers & make a visual inspection from time to time as if it is only 1 of the 2 intake valve cam followers that breaks the engine will still run good enough using the 1 operational intake valve so it can go undetected. From back tracking my data records it appears that this follower broke sometime after a dyno run session that was done on 10-8-19....started getting cylinder misfires during cold starts in mid Nov of same year that set off a P0307 DTC.....some 6 weeks later. I even had the car checked again on the dyno on 12-27-19 w\ this follower apparently already broken (we lost low end HP\TQ vs last dyno session & logs showed slow VCT response at lower RPM's....this is what got me to pull the valve covers to check the VCT solenoids for trash in the screens as this can't be checked no other way or I may have never done this) so I dodged a potential MAJOR engine failure. The only other clue that I had to go on was when monitoring the car thru cold starts after resolving the cylinder misfires (both real & fake) & smoke testing the intake tract & resolving the vacuum leaks found there, was once the PCM went into CL the B2 STFT went way lean (+%) vs B1 STFT (both should go -% for a few seconds before returning to stoich from picking up on OL cold start fuel enrichment) until the ECT >82*F & #7 cylinder kept showing a lot of misfires in Mode 6 data relative to the other cylinders but the #7 cylinder wasn't physically misfiring. Found this was due to air entry into cylinder thru the stationary intake valve's guide which wouldn't seal due to no oiling to the valve stem seal from the busted follower which was not mixing w\ any fuel from air from the intake manifold (where the injector is located) so the cylinder was lean which was spiking the B2 O2 sensor until the stationary valve stem heated up enough to seal the guide clearance sending the air\fuel mix back into balance & was causing the CKP velocity pulse to be lower on #7 cylinder when firing than the others so the PCM thought it was misfiring when it wasn't until the errant air leak stopped. Once I replaced the broken cam follower then ran this test again I saw both banks STFT's go rich (-%) as they should then return to stoich which verified what I typed above. But how many would equate the O2 sensor/STFT spiking/false cylinder misfire data to a broken cam follower? I didn't before...……………..but you can bet I will going forward now as I know what to look for thru FORScan reading the live data...…... Food for thought...……………………... Hope this can help someone else.