I can probably give you some measurements of the missing parts you need for air cleaner parts . I ordered some spare pieces you’re looking for while back from a dealer online besides cpd . Some times you need to just do a google search of a part number and you might get a hit on an old dealer...
Find correct part number for your year bike and put that part number into cpd search block . This is how you buy parts for older Gasgas bikes from cpd if they have them . You manually have to search . There was a water pump gasket change back in early 2000 year range or older in paper but both...
I could show you a few of my Gasgas engines that I personally have split and rebuilt and you probably say same about these . But like ya said it’s a mystery . Maybe someone dropped the pieces in during assembly.
I just changed seals and bushings on my 2010 ec250 with sachs front suspensuon . I don’t recall having any issues .. sorry you were talking about rear sachs . Luckily mines not leaking yet