Boxerworks.com

1. Is it OK on a cold morning and worse when hot?

2. How did you measure the end play of the input shaft?

You have described the classic case of a grabby clutch due to excessive end play of the input shaft.

This info is available on my website.

its the same hot or cold .
input shaft end play as per your site , first thing I looked for .
I shimmed it too tight at first to really see if this was the fault .
regards JIM