South coast is good. I get spare parts off him for mine and as mentioned the individual bits are cheap.
Don’t worry about the guide pins coming out. To give it a good clean they have to. A bit of grease holds them in place when you put it back together anyway.
I got about 4 years out of my i900 (old name for dropzone) doing the self service and cartridge rebuild that’s described on mtbr. Never used new orings, just stripped, cleaned refreshed oil then re-pressurised. Getting the air back in is a faff and takes a few goes to get it right but it does work.
It eventually wouldn’t hold pressure(probably due to worn orings) so southcoast replaced the cartridge, one way bearing, guide pins, seal and even put a remote capable head on it for about £100. Quick turn around and a nice guy to chat to. Gave me back a new post basically ?