Oil proof brush? | Model Engineer : vimarsana.com

Never had a problem with soluble/suds oil and brushes as such. Slideway oil clogs them and swarf and non ferrous chippings stick in the bristles even worse then. A good scrape on the rim of the scap bin and a squeeze in an old towelling rag increases useful life.
The best brushes I have found are the really cheap and nasty 1 1/2 inch paint brushes from the likes of pound shops. We used to have access when in business to a cheap tool warehouse. I bought these things in boxes of a dozen at a time. They each have twice the working life of any branded brush. The very best ones are unpainted handles for this rough work and I have even used these for laying up glassfibre.