Just make sure you also remove the little 6-bolt plate/sump cover of the OD unit when draining so you get all the old fluid out, then clean the magnets on the inside of that cover. Get a new sump cover gasket first - IPD have them separately but don't mention this in their catalog. I've switched to Redline's MTL (synthetic) fluid for our M46's and noted an improvement in shift quality and OD operation.

I use the clutch every time I engage or disengage the OD - I figure this reduces the shock loading on those small OD parts.
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, "my" 94-944 B230FD; plus wifemobile Dodge minivan, hobbycar MGB, and numerous old motorcycles)