I have two A10's which use the same air cleaner element.
I have replaced the original element media in each of them, with a section cut from a K&N element part number TB-0300 (originally designed to suit BSA triple!!).
There is enough material to fit into two A10 air boxes.
Drill out the 4 rivets which retain the original element.
With careful use of silicon sealant, you will be able to totally seal your "new" element in place.
It has rubber surface on each side, to guarantee a seal across the faces.
The K&N cotton based media is much less restrictive (and more efficient at particle removal) than your original media will be at this stage.
It will last your lifetime, and only require cleaning and re-oiling as per K&N's instructions. Use their oil on the element.
Every bike I have used K&N elements on (BSA's, Yamaha 2 and 4 strokes,) has gained horsepower, and you will need to check your jetting.
For example, my plunger A10 gained 3 hp.
Here is the link to the K&N element:
http://www.knfilters.com/search/product.aspx?Prod=TB-0300Next time I have an air box off, I will take some pics & post!
Richard