how to fix my 5 year old APM 6855 50;50 (01) fridge/freezer?

Two nights aho the digital display stared bleeping flashing , and by morning inspite of my efforts to reset both the fridge and the freezer stopped working ! Every thing is spoilt! I called in an engineer who after removing a panel at the back of the freezer said the " gas had leaked and recommended replacement at a phenominal cost! (his quote) It was while frantically searching for a suitable replacement for the space , I found this site discovered I was not alone. I will now turn the appliance off for the next 48 hours but meanwhile can any one out there please advise. I am very suspicios of that "engineer" Thank you