My Stebel Nautilus air horn 139Db lost it's bellow and started to just squawk. I removed it and pulled the horn part off the compressor as it didn't seem to be putting out much air. I sprayed some lube into the air intake but still no joy. The compressor is a sealed unit so out of curiosity I decided to bust it open and I still couldn't see why it was not working. The motor span up fine and the vanes were intact. I bought it in 2015 for $35.00 Au the current price is $39.95 Au.

 I had a look at the place where I got it originally and they had heaps of horns.  https://www.onlineautoparts.com.au/  This time I decided to try a different approach. You can buy high power magnums diaphragm horns 136 Db $32.95 Au a pair or buy them individually without the relay which works out  $16.45 Au for the low tone and $13.70 for the high tone.
 
I decided to go one at a time and bought the low note first, which was pretty good but I decided to go for the second high note. I just pulled off the pathetic OEM horn and the magnum bolted straight on.  The way I originally wired them I had the choice of the nautilus or the OEM. Now I have the choice of one magnum or two.
Regards Martin.