I just finished replacing the brake lines, then bleeding the system, and noticed there is fluid leaking along the bottom of the reservoir where it sits on top of the master cylinder body on the right handle. Looking at a diagram online it looks like it could be this little o-ring between the reservoir and the master cylinder body. It appears the smaller screw which holds the cover down, and another screw from underneath are what are holding the reservoir onto the master cylinder. Once I drain the fluid out of the reservoir it looks like a pretty simple repair to replace the o-ring, but I have been wrong before :-)

Any suggestions or advice?

Yeah thats about it. they can be a bit obstinate because the dried out fluid gets sticky and as  some are getting a bit old be careful not to crush it but you can still get new ones so all would not be lost.

Try and get an OEM O ring. I had all sorts of trouble using what I thought was the same size, but there must ve been a tiny difference in the thickness of the ring as it kept up a weeping seep till I bit the bullet and got a new one. I now don't touch it unless I really really have to. Beware the master cylinders get brittle with age so treat it gently when removing/replacing the O ring.
Good luck
RT

Happened to me.
Simple fix. Use a syringe to empty the reservoir. Easily removed and an original O ring cost £1.10, about $1.50.

Everyone, thanks for the advice and comments. I will let you know how it turns out later this week when I get the part and get it installed.