Motorcycle Repair: 1970 electra glide, brake failure, master cylinder


Question
Hello.  I have two problems:
1) there is a leak in the master cylinder.  small enough that my mechanic says not to worry, but enough of one that over the winter the resevoir was empty when I took it out of storage.  If I replace the master cylinder, I see a large range in prices, from $80 - $200.  WHat should I be looking for in this component?  Also SHould I have the brake lines replaced while I'm at it?  Same question about price range and quality indicators.
2nd question is the bike's speed will drop when I'm cruising at 60 -65 mph to around 50, even though I haven't let up off the throttle.  WHy and what to do about it?

Thank you in advance

Answer
Anytime your master cylinder leaks it should be taken care of. If not, you are taking a chance of a brake failure!
You never said if is was the front or rear master cylinder, but it shouldnt be over $100.00 You dont need to replace the brake line, unless its bad
On the throttle, check the throttle and see if its sticking or the cable is sticking
Good luck and happy riding
Mike