If the original is 7.5/10 or better, then keep and bring it up with clean/polish/touch up. You will never get it perfect, but it will always be seen as an original.
If original is worse than 7.5/10 then do new or replace component. The thing is that classic SS titles are getting over the 30 year age and it is becoming rare to find good original machines. A lot of them have already had cabinet, backglass and playfield re-dos. Some are done too good for my liking and do not have the character of a 70/80s machine. For example some playfields are clear coated to a glass like finish which looks good but not authentic.
