I had the same problem on a '01 V70: the dealer never really solved it, simply kept "oiling" at each service, which helped a little. When the replacement '04 V70 showed the same fault after three months, I insisted in having the gearbox removed and re-greased under warranty. Now, after 4 years and nearly 150000km, it's still ok. It's probably worth asking the dealer to do his "oiling" upon service, they should offer it for free since it's a well known problem. Another trick which worked for me was shifting into third gear before going into reverse, rather than directly from neutral into rev.