Supercuda's on the way back...after18 years!

Ok so a few posts back I mentioned that I had changed out the Brad Penn break -in oil and poured in fresh synthetic 5W30 and a new filter. I immediately started getting a knocking noise that I isolated down to a lifter on the driver side using a stethoscope. Thinking I had a bad lifter, I took the top off the engine (plus had to remove the head to get the lifter out) and replaced the lifter. Put the engine back together and... another lifter on the other side started making noise! I couldn't make any sense of this so, in desperation, I changed the oil to a Castrol 5W 30 non-synthetic and another new filter. (same brand).

Started the engine...perfect!! No Noise! WTF..!!
I have been trying to get an answer to this for months and have had everyone here at work involved including two Red Seal Certified Mechanics and no one could make any sense of this.
Last week, I had the opportunity to speak with an Oil Rep and I asked him what he thought. Here's the answer and the solution in a nutshell.
He told me that the oil I used , Mercedes Benz 5W 30 is specially formulated for those engines only. I read the bottle, it says so right on there!! He must be correct as when I changed the oil out, the problem disappeared. Must be something in the formulation that won't let the lifters pump up correctly.

Anyway , as has been said on this Forum many , many times, don't assume anything.. Read the Fuc#ING instructions/labels before doing anything!! Lesson learned the hard, expensive way for me.. again!!