Seems early to have leak there....a shop should charge about $90 to fix.....but if I had my choice I would do it myself. I had a Volvo independent shop do mine mid winter last year and they screwed up royally...after three atempts the leak finally stopped, but three weeks later my differential self destructed because the front pinion bearings self munched....I suspect the idiot mech. tried to shift the pinion to get to a better wear location..(ie no groove) and screwed up the preload...This should have been an easy job.

Throw away or return the Haynes manual and buy a Bentley or the Volvo books.