I fly my X5C-1 a lot (just about every day) and haven't had that problem (yet).
Something to do with your flying habits or battery charging habits may be affecting motor life.
More information needed.
1). How old is the quad and approximately how much flying time is on it?
2). Describe your normal flying style...(acrobat, slow & steady etc)
3). How old are your batteries?
4). Do you usually run in HIGH mode all the time?
5). Do you like to do "flips"?
6). Are you using a fast charger?
You can check the resistance across the motors to tell if they are bad or going bad. As they go bad, resistance goes up. Check the resistance on NEW motors BEFORE you use them as a reference point.
Also, if your charger is not fully charging the batteries, the lower voltage will put more strain on the motors. Are you using a fast charger? (Not good)
I have a feeling it's time to get new batteries also for you.
Heat kills them. If they are not flat but are "puffy" at ALL...get new ones.
Try this (assuming you have a VOM)
Charge the batteries fully.
Immediately after they reach full charge feel them. They should not be hot at all.
Barely warm. If they are warm or hot, you are charging them too fast which shortens their life. My chargers take 90 minutes and the temperature never changes. They stay cool.
On the batteries (on the white connector) there are two slots on one site where you can see silver. You can touch the VOM probes there to check their voltage. After they have sat (after charging) overnight, check the voltage the next day. They should be over 4 volts even after sitting for a day or two. Mine are like 4.18, 4.14 after 24 hours.