That’s how it first started; the oil pressure would normally be just below 60 psi at 3,000 revs continuous driving. The first indication of any problem was when it dropped to 40 psi at 3,000 revs. 40 psi is probably within the supras specification, but as I normally would run at 60 psi I started to get concerned. The obvious thing to do was to change the oil and oil filter; this improved the oil pressure but only for a short time.Then the slight knocking started, the rest is history. I think the first thing to do is to open up the oil filter and to see what's inside; this should give you some idea of any internal engine wear. Apparently its common practice to open up the oil filter for inspection on aircraft engines. I suppose when you think about it, it makes sense.