Is it possible to dismantle and refurbish an original 870 Technic motor?
While it is important to keep old and rare Lego pieces in good condition;
looking at the part in LDCAD, it does not look like there are any screws to take it to pieces, so I think it is internally clipped together, where such clips cannot be pulled back apart again after they snap in. Several Lego motors use these clips.

However since you cannot see them it is debatable weather it matters if they are broken/cut because you can probably super glue it back together and since the glue will be on the inside you won't see that either, but I will leave that risk up to you :)