I recently managed to obtain a number of Cassese stock items from the French liquidators that included some parts for the Cs810 underpinner.
Amongst these items were 5 (very rare to obtain) official Cassese firing button upgrade kits:
(comes with printed fitting instructions)
Link to item: CS810 Firing Button Link
Amongst these items were 5 (very rare to obtain) official Cassese firing button upgrade kits:
(comes with printed fitting instructions)
Link to item: CS810 Firing Button Link