My NH36 modded SKX009... which I have broken twice.
This is the 2nd Seiko I bought after getting more into dive watches, I bought this new for the princely sum of $125.
Unfortunately about 2yrs later I had a "mishap" while wearing this watch and fairly well stuffed the 7s26 movement... I decided to keep the orig movement so that if value warrants eventually I could get it serviced and restored to "stock".. so it is in the box somewhere here.
I bought a NH36 and stem / crown and swapped it out (eventually after waiting for replacement seconds hand after fairly truly destroying the seconds hand on my first watch making adventure.) Anyway the swap was done and I was quite pleased with myself.
about 2yrs later I had a "mishap" and this watch now gains about 5mins a day ... So eventually I need to just get another NH36 and swap it again..
I like dive watches.. Seiko, Citizen, Orient.. etc
You can regulate the watch to bring the rate back to acceptable specs. The watch may also be magnetised, that often causes time gain if I remember correctly.
I always recommend checking to see if the movement is magnetized before doing anything else. Literal pennies to fix, or mist watchmakers will charge a basic fee for degaussing.
Beautiful Seiko ! Keep up the good work. Any mistakes are inevitable and a learning experience. Good luck.