""""1980 242 DL with an M45 manual""""
This a a 4 speed tranny without an Over Drive --- The M46 has an OD attached to the rear.
.The M47 is a true 5 Speed found in 1987 and later 240s
Both can use Redline MTL or the Volvo Manual Trans Fluid ---which are more or less the same specs.
If your 1980 has an M46-- with a OD, then what Dave says AT trans fluid - is what you should use... because of the OD. And this would be different than the fluid for the M47.
I have a 1980 DL with the 4Speed, and an 87 245 with a 5sp
http://www.vivaperformance.com/genuine-volvo-manual-transmission-fluid/
https://www.ipdusa.com/products/6980/106979-redline-mtl-manual-transmission-oil
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