When I had that cold temp slip in first gear (it can get into the high 40 degree F at night and in the early mornings here in CA) changing the Filter and Fluid appeared to have fixed that. However, just about 1 year later my B2 Piston broke.

I don't know if the slip was a precursor to the B2 Piston breaking.

Does it also slip in reverse?

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84 300D, 82 Volvo 244Gl Diesel