I used to have a Mitsubishi 3000GT for which the manual stated 10W40 oil should be used, however a lot owners used to swear by this 10W50 oil which has a slightly higher viscosity at temperature
https://www.ebay.co.uk/itm/174774140...mis&media=COPY
It might be just enough to boost your oil pressure for a while. It is a bit pricey though! I should state that I have never personally used it in a KV6, so can't confirm any effects, positive or negative.