Broken Speedy Pro

Hi, I was hoping for little advice on my Speedster Pro 1861. I bought it used just over a year ago and the watch had just received a full service from Swiss Time Servicing (STS). The watch has run really well during the time I've had it and I wear it daily.
Last night I noticed it had stopped so I popped the crown out to set the time and it felt alittle tighter than usual to get the hands moving, I'm not 100% sure but think I saw the seconds timer (not the chrono) move backwards a few seconds which I've never seen before.
I set the time and then put the crown back in to continue winding the watch, it needed about 1/4 of the turns needed to get to full wind.
The watch keeps good time when its running but obviously has a problem winding and isn't getting anywhere near the runtime I should be getting, I'd guess maybe 8 hours or less.
Does anyone have any idea what might have happened? I've been researching it tonight and maybe it's a broken mainspring with enough remaining for a few hours running time?

It was from a highstreet seller and there was an STS card with the serial number on. I called STS when I bought the watch and had a chat with them and it all checked out.

Oh wow, I should have checked that first, could have sworn it was 12 months. Thanks for the heads up

Just dug out the Warranty Card, Full Service May 23, 24 months warranty. I can go to bed and sleep little easier. Thank you padders and JwRosenthal