The oil issue for the
6 speed has been discussed at length - notably with info from Smallblock454.The general conclusion for both 5 & 6 speed is that anything other than the correct spec is an ill-informed and expensive choice.Following is for 6 six speed only.
2nd gear, hard to shift after tranny oil change
2nd gear issues
Gearbox 8620-1003 for Boxtser S 04/2003