Need some advice please gang. Before I pour in the red liquid gold that is Redline’s finest gear oil, I was thinking of getting the car properly warmed up, putting her on stands, draining the oil and then doing a flush by filling, then running through the gears while on the stands, then draining again. My question is, would it be OK to use a tin of 20w50 classic engine oil I have sitting around (for the flush only) or should I be buying cheapo GL4 for this purpose? Everything I’ve read says engine oil is even tougher stuff and the classic oil is designed to be kind to yellow metals / more viscous. Or do I just pour it in and change oil again in a couple of thousand miles!? What think yea oh wise ones?