O-rings, or toric rings, can easily be found at your nearest DIY store, in the plumbing department. You may need to try a few sizes to find the most comfortable for you. It shouldn't be too tight!
You should yes. It works really well (well...in my case). I started in February 2015....a bit over 3 years ago. And I know that to get full erect coverage, Ill probably need another 2 to 3 years...