if its the seals on rocker cover top,they're not a big job to do.think they just prise out with screwdriver. also think sealant has to be used to put new 1's in though.(could be wrong though,anyone?)
what makes garage think its your pistonrings that are to blame? also,the engines supposed to breathe so to speak,thats why you have ventilation valves. how well do you know this garage? trust them?