Abe,

I am very sorry to hear that you are thinking to replace your W107 to R126.
I know newer SL is faster, but old SL has more taste to me.
Also, it is very common that 2 model older MB usually trade higher than 1 model older MB, such as old 280SL is traded higher than our 560SL.
I am believing that our SL market value will go up since brand new SL just released.
So if you could fix this noise, I hope you will keep your nice SL for a little longer.
Please let me ask more about the noise.
Could you tell me where does it come from?

If it is coming from rear section, it could be
a)drive shaft
b)drive shaft joint disk(rear)
c)rear axle
d)transmission mount
e)axle mount
f)sub flame mount
g)exhaust connection and/or muffler mount rubber
h) rear brake disk pads

If it is coming from front section, it could be
a) drive shaft joint disk(front)
b) engine mount
c) sub flame mount
d) front wheel hub bearing
e) transmission
f) front brake disk and pads

Also, it is very common that wheel rim is sometimes hot straight caused by running over stone or something.
Usually, it is very hard to identify by just view test, it must be checked by wheel balancer to spin the rim to see if it is not evenly round.
I know the most of MB dealers are not too friendly to used car owner(they like new car owner or possible owners!), but they have proper tools to find the cause of your noise.
Also, they usually do NOT charge anything for just finding out the problem source, only when you decide them to work on the car.
So, please try the dealer and show them my advise.
Please do not waste your nice SL!

Ezzy.