Found the problem!

I was finally able to remove the timing cover too inspect the timing belt. The good news is that there was no oil inside the cover so the oil seals seems to be OK.

After lining up the timing marks I could see that when the crank and pump pulleys is correct, the cam pulley is about two teeth early. My ecucated guess is that the belt slipped and this is what made the valves hit the pistons and bending the pushrods.