OK, Ill pick up the $120 OPDA assembly..........big question though, do you think the camshaft itself is OK? Are people normally finding that the OPDA gear worn, but the camshaft gear itself to be "OK"? Since the front fenders, grill, radiator,head etc are already off, replacing the cam itself is probably easiest now, but Id rather not have to since the cam lobes and lifters all still look brand new with no wear. Using a flashlight(no mirror unfortunately)looking down the OPDA hole the camshafts own gear looks to be OK.......
The common answer is the OPDA gear is the sacrificial gear and it will wear at an accelerated should something like this occur. I would suspect that everyone who has this problem as a prematurely worn camshaft. Does it need to be changed is yes, however the bigger question is when.
I would suspect that the camshaft has some damage. Less than the OPDA gear because:
1. Leaving for reference, but incorrect. As Rubi pointed out they move at the same speed 1/2 engine speed.
it's larger meaning the smaller OPDA gear will rotate more frequently causing more wear.
2. the OPDA gear wears more by design so that should it wear, it is easier to replace than the cam. I don't know the hardness of each, but that is common practice from what I've learned.
Most of us do not replace the camshaft because of these reasons along with cost and time. If you have the money, time, and feel that now is the time, I won't say don't do it. Just remember you are simple hitting the reset button. Nothing has changed with the OPDA or camshaft. TJJP77 just swapped his camshaft and OPDA and we are all waiting on his results.