UPDATE: I have since sold off all of my Sony gear and moved to Nikon. As with any DIY project, unfamiliarity with tools and process can lead to damage so this post should be construed as theoretical advice only. If you are at all uncomfortable or inexperienced working on DIY electronics projects, please reconsider doing the job yourself. By using this website, you agree to indemnify Sung Park ("the Company") for any and all claims, damages, losses arising out of using the information in this website. The materials on this site are distributed "as is" and appear on the site without express or implied warranties of any kind, except those required by the relevant legislation. In particular the Company makes no warranty as to the accuracy, quality, completeness or applicability of the information provided.
I've put my main A7rii body through a lot this past year, and apparently my somewhat acidic skin doesn't help much. A big chunk had come out of the thumb pad area on the back of the camera body, which proved to be incredibly annoying.
Thankfully, unlike the mark 1 A7 bodies (which had the rubber portion integrated into the back plate), Sony made the smart decision to make the rubber portion a separate part number that is surprisingly cheap at about $35 plus shipping: https://www.encompassparts.com/item/10855597/Sony/X-2591-929-3/Grip_Assy_(795),_Rear
Important: It appears that the back plate and rubber grip is slightly different on the A7ii versus the A7rii. Make sure that you order the A7ii rubber grip part, not the A7rii one as there appear to be subtle differences between the two. The A7rii has more magnesium alloy bracing on the back plate, whereas the A7ii does not seem to have the alloy on the back plate. Also the A7ii grip rubber seems to be attached with a few dabs of epoxy based on the photo I was sent, whereas the A7rii grip rubber does not have epoxy and instead is held on with 3 plastic tabs and the two screws. Perhaps the magnesium alloy on the A7rii back plate offers enough stiffness that the plastic tabs are able to hold it in position better?
Here is a pic of an A7ii back plate with integrated rubber grip alongside an A7r2 rubber grip. If you look closely at the A7ii back plate, you'll see that the rubber grip is held on with semi-permanent plastic rivets that appear to be melted or glued to attach the grip. If you compare it with the A7rii back plate later in this post, you'll see they are different as the A7r2 rubber grip is attached via a couple tension clips and screws and is not permanently mounted to the back plate.