Hummm......... interesting info here. We still need an idea of mileage on the engine.
Oil pressure while cold is not a indication of oil pressure when hot so I'm going to discount that. I've seen engines that had full oil pressure while running cold and nothing showing on the gauge when hot. I imagine yours is somewhere in between those two areas.
Can't agree that one of our engines will go 200K before needing a rebuild and 150K is really pushing it. Average cylinder wear, with really good service work, is about .001'' per 10,000 miles. The question arises, how well was your car maintained over its entire working life? Modern oils have improved greatly since 1966 but how do we know what was done 40 years ago? Most cars I see that need a rebuild are generally over or around 100,000 miles up to 130,000 miles. Cylinder wear will be in the .005 - .007 range which may not sound like a lot but at that amount your piston rings will start to vibrate ( my belief ) while trying to expand and contract against the upper cylinder walls at higher engine speeds; which is why I recommend keeping it under 4,000 RPM. A compression ring will eventually snap off about 40 mm from the ring gap. Keep in mind that the piston grooves will become worn as well and this will add to the overall movement of your top compression ring. The broken part of the ring will flop around horizontally until the piston groove wears enough that the broken ring will start to move into more of an up and down position. Eventually the broken ring will gouge out a spot on your cylinder wall and then it will pop out the top side of your piston. If the engine is at idle you will hear a very loud noise that will sound like a valve hitting a piston. If you are driving at road speed you will hear what sounds like pinging. It will last less than a mile of driving and then it will go away. This is what I call the '' death rattle '' and your engine is in fact, dead. The noise you will hear when this happens is caused when that piece of piston ring starts bouncing around in the chamber between the moving piston and the cylinder head.
So, look at the cylinder walls carefully and inspect for scoring and wear. Without removing all of the pistons there's no way to know what condition your pistons and bearings are in. If you have a weak rod bearing, failure will happen after a valve job if the bottom end isn't looked at. If your pistons are in good condition you could use them again, get new rings and bearings, and put it back to work. I would highly recommend a new oil pump, crank gear and rails if you go that far.
You should also be aware that late 230SL's now use stepped pistons. It's not what the engine came with but that's all that's available now. I think I have a set of first oversize.
