Residue marks on washing from Bosch WFK2801?

Hi we have a 2nd hand Bosch WFK2801 - it's a great machine,but today we have had mud or scum type of marks on the washing.
The sealing door rubber is clean but I notice muck that has not rinsed away between the inner & outer drums and a tiny bit round edges of the washing drum.
How easy would the inner be removed from the outer to clean? Instuctions would be very appreciated. I notice that there are 'clips' on the outer drum close to the door when the lid is removed.
Would an empty wash with 'bicarb' assist???
THANKS!