As above the gearbox and compression parts are very good.
I have owned 3 and built others for customers to varying levels but you don’t need much.
The gear set is also very good quality - DO NOT CHANGE THEM!
This is all you want parts wise;
ZCI high torque motor with ICS pinion
Prometheus EG barrel 455mm
Prometheus type 2 cylinder
Renew the piston head O ring
Nice bucking and nub
Gate PicoAAB
Alpha Wire 16awg
11.1V LiPo
New ICS spring if it’s sat around for years.
Renew ICS parts in the lower receiver related to the cut off lever - I cannot remember the part numbers but if you look in your manual at the parts diagram you can order them direct from ICS.
This keeps fire selector semi issues at bay.
Free upgrades / work;
Re shim the gearbox.
Set motor height.
Polish / de burr the gearbox shell.
Check all air seals.
Support the inner barrel agains vibration.
Shim the hop unit toward the gearbox 0.5mm-0.75mm, this fixes double feed.
Icing on the cake, semi pro job;
Ditch the trigger contact assy and replace with a micro switch, short stroke the trigger.
Yes I like the ICS L85 ?