A new muffler was installed in April 1976 at Bartholomew’s Advance Muffler & Auto Service in Pasadena, California. While no mileage is given I would guess this to be at about 42,000 miles. Amazingly, this company still exists.
Parts for the MGB muffler system came to $92.75 with $5.57 tax and $20 labor for a total of $118.32.
It’s hard to imagine replacing a muffler on a modern car this often but like everything in the automotive world we have it very easy these days!