330cl engine ecm error, swing brake sticking and other nice warnings

we bought thgis excavator 2 years ago and it ran and operated fine for the last season.the machine sat all last winter and was moved to a job in march. it ran fine for about 4 weeks then the swing brake began to stick and the machine would only swing if switched to " fine swing " then the engine ecm error popped up on the screen followed by a low oil pressure text and warning alarm. cat came down .looked it over and said the machine was fine...pressures are all good but they did replace a wiring harness that they claimed was cause of all the issues. machine ran fine yesterday then today same exact problems. after an hour of use the ecm and low oil pressure came on again. boss said to ignore it and keep running....swing brake began to stick and then the hydraulic pressure for the stick would drop and the machine would return to idle while i was digging. the stick would move very slowly for a cycle or 2 . had to switch it to manual throttle so i could get it back near the road. once the machine sat for a few hours it ran fine again untill it reached operating temp...then the same problems. anyone have any advice ? brian