A few things to be aware of:

1) The attachment to the frame on Original Equipment mufflers included a bracket that was like a bridge from the frame to the mufflers. If your old mufflers are original, remove the screws at the frame first and leave the bracket in place for starters. Many replacement mufflers do not use the bracket because the tangs are welded to the muffler itself. No sense in fighting the screws in the muffler needlessly. If you need the bracket, it would be easier to deal with the screws on the workbench as opposed to "on the bike".

2) At a tech day, I have observed a muffler that could not be separated from the header pipe with the clamp loosened. Be prepared to destroy the old muffler to remove it. In this case, I would use a hammer and chisel to peel the muffler flange away from the header. 

3) Penetrating oil and/or heat can be helpful in dealing with rusted or stuck screws and bolts. Be careful with using heat. I usually find it necessary to heat to reddish glow to release a very resistant fastener. You wouldn't want to blister any paint or start a fire. 

I am sorry I am not up on what replacement mufflers are available for your bike at this time.  Check with Max BMW, EME, Boxer two valve.  

However, as long as you stick with a stock style replacement set, you should have no problems.  St.

Thanks, I got a pair from Euro Motor Electrics.

They look like what mounted. I May need to remove the drivers left foot peg to get to the clamp bolt to the header pipe.  I don't mind destroying the old one as long as I don't mangle that pipe!  Thanks for the heads up On the penetrating oil and heat.

James, I believe that was my bike at the Mundelein tech session.  You guys were diving into changing the tires and balancing both wheels.  It was impressive!

Posted by: @8053

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A few things to be aware of:

2) At a tech day, I have observed a muffler that could not be separated from the header pipe with the clamp loosened. Be prepared to destroy the old muffler to remove it. In this case, I would use a hammer and chisel to peel the muffler flange away from the header.

Take the same Never-Seize compound that you use on your finned exhaust nuts and spread that liberally onto the inside of the new muffler input spigots. That will delay the very troublesome bonding that tends to weld the muffler to the exhaust pipe, and could save you hours of headache in the future. 

(Worthless, irrelevant comment). Sometimes it just strikes me as funny. Us guys with these old bikes. When we put things together, we either use “Anti-Seize” so it won’t stick, or “Loc-Tite” to make it stick …. we are never happy with it just plain. 

Well, I let penetrating oil work for a couple of days, tried a pipe wrench... It ain't budging.  Guess I'll employ some kind of metal cutting tool and just peel it back, And hopefully not damage the mating surface of the header.

Is it the same left muffler as at the Mundelein tech day? As I recall, nobody was interested in applying potentially destructive measures to it. This is where I would avoid a power tool like a cut-off wheel or Dremel. It would be easy to slip and maybe injure the header. A sharpened, FLAT chisel applied directly to the edge of the muffler flange should take a bite and avoid involvement with the RADIUSED contour of the header pipe. After a few whacks, the shock wave generated by the impact might serve to release what ever mystical attractive force your muffler has developed with the header. If you want to use a powered cut off wheel, you could cut the muffler off completely just down stream from the end of the header. That would leave you with a much smaller section of pipe to deal with. Maybe you could enlist the assistance of one of the members from the tech day, or attend the next one in May.

Also,... don't go whaling on it. With repeated light blows you can see the chisel dig in to the edge. Be mindful that the only other thing holding up the header is the exhaust port on the head. You wouldn't want to put too much stress on that. I worked in a muffler shop when I was much younger. We had to use a chisel where heating a joint to cherry red was ill advised. 

I  put a cut off wheel on an angle grinder and sliced it off about 6 inches downstream from the header clamp as you suggested.   Then, with hammer and chisel, inched my way back toward the header where it Eventually started to spin and I just pulled it off. End of pipe looks perfect!  Thanks for all the hand holding!  It's supposed to be mid-60s here in Evanston and I can't wait to get the new one on, fire it up and listen.  The right one curiously has no rust holes.  But I think I'll replace it tomorrow because the finish on the new one does not have as high a gloss and I want them matched.  Maybe polishing.  We'll see.