I don't believe there is a gasket used. I like Clark's inserts, some here like others better.
Will the gen size dial fit the case?
As it comes, the GMT hand works with the hour hand but geared to make one complete revolution while the hour hand makes two. It is adjustable, so usable for other time zones.
The gen GMT hand is 1.8mm. The modded ETA/Asian 2836/2846 and DG 3804B are usually 2.0mm, some bigger. The gen hand cannot be broached to 2.0mm, it will break the sleeve. I have successfully broached the gen hand to 1.9mm, and turned the GMT pinion down to fit it.
Gen Rolex hands will not fit the ETA movement. Most parts suppliers we use have gen style hands for Rolex Tudor that will fit the ETA. I know Clark's has the Tudor Submariner hands, but I don't believe he has them 'aged'. Rafflestime may have the aged ones.