I use a very large pair of Channelocks with the trans in park to loosen/tighten the nut.

Uberwasser is correct. But I've never worked on a driveshaft where I couldn't slide the splines with some prying force, even with the nut tightened.

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1981 300TD 310k miles
1970 280sel 172k miles
1966 230 Fintail 162k miles

"Where are we going? And why am I in this hand basket?"