If these are red top motors, they are AC motors, if you remove the encoder, although it is keyed, make sure you mark it where original tabs are as this is also the commutation device.
If you can get in there with a Q-tip and de-natured alcohol, wipe the disk off as best as possible, If you are adventurous you can carefully lift back the top board and clean the photo cells, mark where the board is, but IRC, you may have to unsolder the wires on this model.
Take care as they are expensive encoders, and cannot be subbed.
The encoder is secured by a 4mm screw down the centre.
Al..