Andronikos, I took some of your pictures and blew them up 200%. It sure looks likes some of those lifters are adjusted wrong. Look at cylinder #6 lifters, the second pair from the front on the drives side. Where the push rod sets in the lifter plunger it looks like one plunger is a lot lower below the retainer clip than the other lifter. The adjustment normally is 1/2 turn when the lifter is on the base circle. Yes the
oil can bleed out from setting but not that much so soon. Normally that 1/2 turn pushes the plunger that amount below the retaining clip. They should all look about the same.