Bicycle Mechanics - Giant Cypress Twist-grip shifter problem

I just bought a used Giant Cypress bike on Craig's List. I love the bike but today the right twist-grip shifter started mal-functioning. The left shifter clicks as the gears shift up and down but I don't hear the clicking sound from the right shifter and when I shift down the shifter does not stay in gear. It slips down to the highest gear as soon as I let go of the shifter.

Can someone point me in the right direction? Is something broken or is something in need of an adjustment?

I wanted to try fixing this myself before I take it to a bike shop.

Thanks in advance for any help anyone can share that might point me in the right direction.

You might get it to work by flushing it out with WD40, but new ones are cheap enough it's not worth spending too much time on.

I would avoid WD40 or other high-solvent treatment, as the twist shifter's internal components are likely plastic. However, as w points out, a whole new shifter should only cost $10-20.

Where would I be able to find one of these shifters? What's a good place on the internet to find these kinds of parts?

I ride a hybrid with many components the same as your Cypress, including the Sram MRX twistgrip shifters. About a year ago (3000 miles on it) the right twistshifter on the bike did the same thing as yours. I bought a replacement at LBS for about $15 and put it on myself, as the included directions were easily understood. I took the old one apart, determined that a spring (shaped similar to a ~) was no longer operable because a plastic nub (part of the housing, but internal) had worn down. Thus the spring could no longer hold a selected gear. About a month later I had to replace the left twistgrip, for the same reason. The new twistshifter comes with a cable, so just feed it thru the cablehousing, and attach to deraileur. Now that I thought about it, I recall that the problem first started with a cracked housing, which I kept taped until the shifter finally failed.

cl - as do suggests, probably best just to buy a complete left and right shifter pair. First, confirm that your left shifter/front crankset have 3 gears (this is standard). Second, count how many gears the right shifter and rear gear cassette have. This will likely be 7 or 8, but perhaps 9. You'll need to buy a shifter pair with the correct right/rear gear count:
Here are some decent choices:
For 7 gears: http://www.rei.com/product/737410 or http://www.bikeman.com/LD4751.html
For 8 gears: http://www.rei.com/product/737409 or http://www.bikeman.com/LD4750.html
For 9 gears: http://aebike.com/page.cfm?PageID=30&action=details&sku=LD2685 or http://www.bikeman.com/LD2685.html
Good luck!

THANKS SO MUCH FOR ALL THE RESPONSES! I got the shifter at my LBS, installed it, and it works great!