Use a 40 body oil... 5W40, 10W40 or 15W40.
Monitor for oil consumption and oil contamination.
If you have oil consumption, change the PCV valve. If oil consumption continues, you are losing oil through either the valve seals or the piston ring. Both involve some cash flow to rectify.
By oil contamination, I refer to the sludge buildup in the engine... Lots of guys love to use 20W50, the best sludge making oil on the market, regardless of brand. Monitor the colour of the oil for carbon buildup. If it turns dark quickly, change the oil. The 40 body oil will clean up the mess left by 20W50, if this is want was previously used.
Avoid engine flushes as these are harsh chemicals which may lead to engine failure if incorrectly used.
If you did use 20W50 for an extended period, I recommend either Valvoline or Delo 15W40 and a Luberfiner filter. Monitor as explained above and replace the oil as required.