I just spent several days researching MW ovens, read the reviews at the major retailers, the overwhelming majority of owners had ovens that lasted 15-20yrs without a problem, then they replaced them with current products of the same mfr and had them fail within a few months to just out of warranty. Do yourself a favor and read the owner reviews, you'll learn a lot, Home Depot, Lowes, Best Buy, Amazon are a few that have owner ratings, Consumer Reports had great reviews on some top rated units, but the actual owner reviews didn't match in any way, shape or form.
As to MW leak detectors, there are many available, I got an inexpensive one that is just a bar of clear plastic, it glows red if it detects leaks, I think I paid $15 for it, it detected leaks in our old Kenmore MW that was 25yrs old when I quit using it, still worked tho, the Kenmore that replaced it lasted 4yrs, just bought a Panasonic that has exceptional customer reviews.
Tim