I was faced with a similar conundrum when I rebuild my solid deck 20". The original adjuster was quite flogged so I ordered an extra series 2 adjuster as they are dirt cheap and thought I could see what I could do with it. It needs to be re-drilled to 3/4" (90% certain of size) and the small plastic slide guide on the rear buffed off. Apart from that you just need to align it correctly as the series one tensioner rotates rather than moving on a straight plane.

Has not been an issue for me in 18 months and I mow a lot!

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