Bizhub C253 Colour issue

[copier addict]

I have a customer with a C253 and a few months ago she had an issue where the machine would be printing in colour and part way through the job it would switch to grey scale. This isn't a case where the colour portion of the page disappears, it actually prints the full image just in grey scale. It does it while printing and copying.
At the time I removed the registration section and cleaned the IDC sensors. That seemed to have fixed it until today when she had the same problem
I guess it could be dirty IDC sensors again, and I will clean them when I go to the call, but I was wondering if anyone has had an issue like this.
Any info is greatly appreciated.
Thanks

[copier tech]

I used to see this issue a lot when I worked on these old models.

Clean the ID sensors again & ensure the firmware is up to date.

Also if the image units & ITB are past life can so cause this issue.