The filter is just a mesh screen, not a filter per se. I don't see a reason necessarily to *not* replace it though. Wonder why Volvo would have recommended blowing it out instead?
You can find a kit that includes a filter, O-ring, and pan gasket as a set, this is the easiest way IMO. Tranny service is worth doing, I like to know what it looks like inside the pan anyway. I have used the "transfusion" method as well. Never tried putting an "in" hose in a clean bucket as well as the "out" hose in the dirty bucket to receive old fluid -- I'm not sure it works that way, haven't ever looked at the tranny diagrams but I have always just done it by letting it pump old fluid out a cooler line and adding new through the dipstick tube. I don't know if the trans will "suck" from the other side of the cooler or if it just returns from the cooler circuit back into the sump under pressure from the feed side.
The times when I have wanted to really thoroughly refresh one, I usually start by doing a pan/filter service, drain all fluid out from that point, clean pan and magnets, make sure everything looks cool in there, reseal with new gasket, and fill with new fluid, *then* begin the transfusion process after that. This way you start the job already halfway done and don't waste as much new fluid mixing it in and pumping it out with the old. Good to do this part with the rear wheels off the ground and trans in neutral since ZF doesn't like prolonged idling or revving in P or N when the output shaft is stopped. This way you can just let the rear wheels spin if they want without having to worry.
Seems like most wisdom about these is that synthetic fluid is not worth the money, better to use DexII+ fluid as cheap as you like, and drain/fill often to keep it clean.
297k on the original unit in my DD, still does what it's supposed to, though the 1-2 shift is a little firm at part throttle. They can last a long time if cared for.
