I use a VPN all the time and just learned about WebRTC which can leak your real IP address.
However, a recently discovered security flaw allows remote sites to take advantage of WebRTC (Web Real Time Communication, a feature built in to most browsers) to reveal a user’s true IP address, even if they’re connected to a VPN. As far as we know, sites aren’t taking advantage of the flaw yet, but considering services like Hulu, Spotify, Netflix, and others are taking steps to identify and lock out VPN users, it’s not a stretch to assume they’ll start.
A few lines of code is all it takes to remove the location protection you get from using a VPN, and figure out where you’re actually located and who your internet service provider really is (who can then tie your address back to who you are specifically.) While the vulnerability is primarily browser-based right now, any application that can render web pages (and uses WebRTC) is affected, meaning anyone who wants to can see past your VPN to where you really are and who you really are. Advertisers, data brokers, and governments can use it to peek through your VPN to find out where your connection is really coming from. If you use services like BitTorrent, have a set-top box like a Roku, or just stream music or movies on your computer through a site that’s not available in your country (or you’re an expat and live abroad), the apps and services you use could suddenly stop working.
http://lifehacker.com/how-to-see-if-your-vpn-is-leaking-your-ip-address-and-1685180082
https://www.browserleaks.com/webrtc
I also use the Thunderbird E-mail client so I went into Tools | Options | Advanced | Config Editor.
Now search for media.peerconnection.enabled and set it to false.
I use the Pale Moon browser and as of this time it doesn’t have media.peerconnection.enabled.
Update-
Another thing to consider is your DNS and potential leaks. If you use a VPN I would set this site as your home page so that you can make sure you are tunneling to the location you expect.
https://www.dnsleaktest.com/
Now I would use the extended DNS test. If you see your ISP’s server then your ISP is using transparent DNS servers. You might have to do a Whois on the IP addresses listed from the extended test.
http://whois.domaintools.com/
If you discover that your ISP uses transparent DNS then look here and use the dnsfixsetup program.
https://www.dnsleaktest.com/how-to-fix-a-dns-leak.html