Cheap upgrade that really helps in the long term.......DM5/6/7 Spring detents.
Much better than the stock rubber ones that wear quite quickly, just need to put a small oring on the spring behind the detent and job done.
I've attached a pic to show you, you can buy the detents from all good Dye dealers (
www.Heavenpaintball.co.uk )
Also, the stock wiring harness is flimsy, so again replacing it with better built one (Lucky Europe have them) would be a good idea.
Not the most 'bling' of upgrades, but they do help towards long term reliability.