Gilera Runner VX125 loss of power when riding ?

My Gilera Runner VX125 loses power when im riding it, i recently got it serviced at a garage about 2 months ago but whenever i turn a corner on the bike it just loses power completley. Also when the bike is stationary a sort of white/clearish liquid leaks lightly from what im told is the overflow pipe. Any information on how to overcome this problem will be greatly appreciated.