hi karl
well done on your new mower, looks to be in great condition for its age.
when you say the air cleaner is missing, do you mean the whole housing or just the foam element, you can make your own filter for it if its the foam that's missing, clark rubber sell air filter foam on the roll, so by doing some tracing and looking at jacks pdf you should be able to make one. fine mech can be brought and cut to size if you need it.
a lot of fuel leaks on that model engine are from the fuel bowl, theirs a small spring brass plunger on the bottom of the fuel bowl which is sealed by a rubber seal on the inside of the bowl. being so old they weep fuel, maybe that's where its leaking, fuel leaks can be hard to trace. just something to check and make sure carb bolts are nipped up.

damo