To me, it wouldn't matter how it broke. If it broke on my "watch" I would replace it. I used to housesit when I was homeless (2 years). One family had an antique mantle clock that had to be wound every other day. They gave me step-by-step instructions. Well, I wound it too tightly and broke a spring. Several hundred bucks later, The Clock Doctor had it replaced and working.

It was the right thing to do. This family appreciated it and recommended me to several families who hired me to to housesit.

The right thing is usually the easiest. No having to come up with excuses or rationalizations. No worry about a friendship being damaged, etc. Replace it. Keep the receipt. If they don't want it, take it back and get a refund.