........Apparently it's not such a good idea to use synthetic oils on the old (design) Buick block......
I second that, and also note that whatever oil you use should have adequate ZDDP additive. This may not be an issue in UK/EU, but here in USA most current engine oils don't have enough because they took out the additive citing potential cat. damage..........to quote Lorne at Gomog: Flat tappet engines require ZDDP. Of course flat tappet engines are no
longer produced for many years (outside of farm equipment and your Plus 8 V8) In 2004, the US government phased in a requirement for manufacturers to guarantee a catalytic converter life of 10 years or 100,000+ miles. As ZDDP, the most common engine additive since the 1920s, can coat cats over a long period, the US car manufacturers, pressured the oil companies to remove it.
