Not knowing what has been done and having been told by Volspec that 10w40 should be used, I would change it asap. They said there had been a few clutch problems but did not go into any detail as the instruction was from Volvo Penta. If the oil currently in the box is red I would assume this is ATF. I dont know of an engine oil that is red. The oil companies usually use different colours to identify the grade and red is auto transmission sometimes used in gearboxes.

    What I did is – firstly when you suck the ATF out, about a pint stays in the gearbox but you can add the engine oil and it will mix (i’m told). I decided to suck out the ATF and filled with 10W40. I then ran the engine in drive for a short while to mix the oil and then changed it again. I now intend to change the gearbox oil every year, the same as the engine oil. I used to change the ATF every 2 years but multigrade oil breaks down with time. You have to wait for the oil to settle as it does foam and you can think it is up to the correct level but isn’t. Oil level must be non foamed up before checking.