Place a saved search on flea bay and reasonably priced part will usually pop up after awhile.
I prefer the oblong cast mufflers for those saws instead of the round muffler.
The oblong rectangular cast type Mac mufflers to me have a better sound and are more bullet proof than the round ones and your can prime the saw easily for a cold start by dumping little bit of mixed fuel straight into the muffler. (direct straight shot through the muffler into the cylinder)
https://www.ebay.com/itm/McCulloch-Chainsaw-Exhaust-Muffler-1-50-1-60-1-70-1-80-250-380-1-63-1-41-1-51/181282935176?hash=item2a354e1188:g:U80AAMXQVERSrnXB
https://www.ebay.com/itm/mcculloch-chainsaw-exhaust-muffler/132441198671?hash=item1ed61c504f:g9wAAOSw0W5aOstv
https://www.ebay.com/itm/McCULLOCH-...782036?hash=item51fe0f8954:g:MlQAAOSw~RNZptCm
I've got some of them old Mac's 1-43's, 1-46's, etc, all running.
Would you be interested in a good running 1-53? (or any of the 1-40, 1-50 series of Macs)
I do not have any individual parts for sale because I'm still in need of my spare parts for my saws.
I only use the old heavy mac's of mine in the wood lot when I get a big log down occasionally and just got through this last fall starting and running all of them then dumping the fuel and running them dry for re-storage.
You will have to be careful and not look at the name VINTAGE and Kart engine Mac's when buying parts, when they use these terms it allows them to jack up their junk parts prices.
Sometimes you can find good info here about Mac and other chainsaw parts and general info about all the models of macs that a part will exchange.
https://store.chainsawr.com/
and that little rubber/plastic cover is more important that first appears. Any dust that goes into that H/L jet adjust opening bypasses the air filter and is headed for the carb intake. You can temporary block it off with a piece of tape. The Stainless steel type AC tape will stick to that area real good.