Thank you for the confirmation and suggestion.  I'm not sure if it will work in the Pirate kit as the motors are “L” shaped in that kit.  Can you advise on your suggested product and if it will fit in the Pirate kit?  Thanks!

Looking further in the catalog I see https://www.dfrobot.com/product-1458.html which has an encoder..  But other than the mention of a metal shaft, there is no indication if the gears inside are plastic or metal.  Can someone confirm the construction material of the gears?  thanks.

Thank you.  Those look exactly like the ones that came in the kit.  And based on the description given on the amazon listing, are not with metal gears nor the encoders I'm looking for.  

Specifically I'm looking for compatible form factor, but with metal gears and rotary encoder.

This listing: https://wiki.dfrobot.com/Micro_DC_Motor_with_Encoder-SJ02_SKU__FIT0458 has the encoder, but no indication of the material of the gears.  

Same thing for this one: https://wiki.dfrobot.com/Micro_DC_Motor_with_Encoder-SJ01_SKU__FIT0450

Unknown if the gears are metal.