The dealer should be able to perform a "drain and fill", which will replace about 5 litres of the fluid. I did this myself on my 2011 petrol, following the procedure from an online service manual. It's not difficult, just a bit of a faff. You do need an obd dongle called obd link lx to read the CVT fluid temperature though. Subaru outback.org has a DIY guide too. I think yours might be a second generation CVT and slightly different to mine, with different spec fluid. My spec was ns2, and there's plenty of it about, I used mannol, but make sure it's for CVT s with metal belts.