I got a leak on my shimano 105 R7020 STI

According to the ST-7020R exploded diagram at https://dassets.shimano.com/content/dam/global/cg1SHICCycling/final/ev/ev/EV-ST-R7020-4341C.pdf

That part doesn't exist as a removable part, hence why you need to confirm your exact shifter part number.

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For completeness - the dealer manual is at https://si.shimano.com/api/publish/storage/pdf/en/dm/RADBR01/DM-RADBR01-07-ENG.pdf and a browse through shows no mention of removing that plate.

The sad part is. That part is not replaceable. It's not that tough when you push your piston. That reservoir will pop and mineral oil start leaking. I believe that it should be replaceable but I found no information what so ever. You will need to replace the whole shifter itself.

I think this is the part you are looking for:

• Y0C698060 Right hand lid unit
• Y0C598030 Left hand lid unit

The rubber diaphragms, item 17, have the part numbers:

• Y0C678000 (right hand)
• Y0C578000 (left hand)

ST-RX600 Diagram showing these parts highlighted:

ST-R7020 Diagram showing similar part names on the R7020 unit specifically: