Your car & motor is now twenty- seven years old the motor probably has never been redone in all those years,why don't you try some good old dino oil (Valvoline Racing VR1 20w-50.You migth pick up 1 to 11/2 bars of oil pressure with it.
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83-944 show room -sold___New ride 93-968 with SC steering wheel-ROW signal ligths- Susp M030 mods lowered,Porsche VA springs- Adjustable struts - Bilstein inserts - Bilstein sport rear -LSD -riding on Cup 1 wheels 17x8 frt 17x9.5 rear road contact Falken 452/ 225-45 ZR Front 255-40 ZR Rear -- Motor Mods /chip /K&N / mod air boxe just love the handling & power