i got a trade leaflet from a guy who sells stuff that works
one of those things is Pro-ma (mlm) MBL8 oil additive, he claims in his experience (here comes the 80/20 rule!) 80% are fixed after adding this stuff, another 10% take up to a 1000km to fix - the remainng 10% are stuffed and need replacing
I have seen this stuff and their other products in the past do some pretty amazing things. Even seen a Toyota dealership stock it on their shelves .. and it is a multi level marketing product !!