Sram X9 rear mech and shifter on Sram 9-speed block.
The mech is nearly new to replace an X7 which had too much play.
When cycling along the mech will not shift into the three largest cogs, but if you turn the bike upside down and shift from 11T upto 32T it does so perfectly. Indexing all perfect and it does not ghost shift.
Am planning to replace cable but if stuck or frayed I would expect it to not drop into the smallest cogs when tension was released.
Could the shifter be the problem and can I take these apart?
When servicing the Magura brakes some mineral oil ‘could’ have possibly seeped in however unlikely that sounds.

Early type X9 shifter rebuild.
Later type X9 shifter rebuild.

Thanks Gary will give it a strip and check all is ok.