I have a 1995 318i automatic, 124,000 kms, that needs an original stock
muffler replacement ( it's loud )....thing is, it'll be $400 CDN to replace,
and I have to wait a month so I can afford to have it done.
My question: Will driving the car for another month with the old muffler do
any damage to the engine, or catylitic-coverter ?

thanks

Defenatly no. It only helps the perfomance and fuel economy. My advice dont get the original piecea shit muffler. get a flowmaster or magnaflow ($100) and install yourself or get the shop to instal. ($200 max for everything.) Just clamp it, dont weld shit on there. It will open up your hp a bit.

F@%k original BMW mufflers!