Heres a cheap filter you can use for a Stilko SK-13. Take a Wix 51300 (can be bought for less than $10) pry the ring and rubber gasket off the hole in the cylinder and take a ball peen hammer backside and gently knock the metal housing back a little and it fits doesnt exactly fill the hole completely but its a metal filter and shouldnt come apart or crush. Heres the pics to show what I'm talking about.
Is that Stilko supposed to use a toilet paper roll? It looks a little different than the one I have...
Yes it is there 2 different kinds that Ive seen one like in the pic where its held together with a nut on top that threads into the cylinder or the other kind that has a long bolt that comes all the way through the housing from the bottom.
Have a friend thats run one havent heard any complaints the filter insert is really sturdy especially since its metal and not completely paper. Dont have my car running right now so it will be spring before I test it first hand. Just figured it out prowling around at the parts store looking for something else.