Conditioning for automotive electronics
Your SA's can handle 500 W transients.  Whoa!  Change R1 to 100k, change C1 to 0.1 uF high-quality*, change both SA's to boring old 1N4148's (yes, non-Zener, you don't need the Zenerissitude), the op-amp now has 100k in series with it and will be fine) and call it a day.  If you really require the high accuracy you describe, make sure the 0.1 uF is high-quality, very low leakage etc.  You see I kept your R1-C1 time constant the same, but now the load and components are much more suited.  The op-amp input is &lt; 1 pA (yes pico-ampere) so it is very high-impedance.