I have a very old variable speed model. The coupler is the weak spot. I ordered a few couplers years ago to have a spare on hand. Well the tool coupler gave out and the spares became brittle over time and useless. So I too went the tubing route. This was quite a few years ago. Still going strong but now I get a slight vibration until it gets up to max speed. Once it gets to top speed it is super smooth. I need to open it up for a look see. A very handy tool. I use it often.