Rear Caliper Seals Installation

[Dimond]

R1200GS 2015 - FYI: The design of the rear caliper pistons and parts availability seems consistent across all the model lines (i.e., not unique to only the GS)

I am intending to install new piston seals. Kit costs $40. The rear pistons have a 'bakelite' insert (the INSERT) in the piston that covers the 'hole' in the top of the piston and faces the brake pad. The insert has a mall weep hole that is open to the interior of the piston - which I damaged when I inserted my metal pick to pull it out. My dealer says that they don't sell 'pistons' for the rear caliper on this bike but $700 to $800 will get me a new one - installed. I don't think this INSERT is essential and plan to grind it smooth with my dremel, replace the seals, and go ride! However, not knowing the purpose of this INSERT I am unsure that I am doing the proper thing. What is the purpose of this INSERT? What would you do? Thanks!

PS - Looking at the BMW Parts Fiche it looks like BMW sold pistons for the DOHC (2014 and before) but they don't sell them now. Seems like they sell piston for the front brakes - all models - even now. There is some reason that BMW 'switched' piston to 'an insert, but not sure why that is?