Drupal module development

Hi, I am looking for some help fixing a glitch in the drupal module "Delivery Timeslot for Ubercart" - http://drupal.org/project/uc_deliverytimeslot. I've described the issue here http://drupal.org/node/1217476 but it looks like the module is no longer maintained.

Here is the description of the problem

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if you don't select a delivery timeslot on the checkout page, you get bounced back to the checkout page with a message "please select a delivery timeslot" - but the other fields on the checkout page that the customer had already filled in are now blank - address details, payment options etc.

I've loked at this long and hard and I am kind of stuck, it looks like the code is using "drupal_goto('cart/checkout');" to send users back to the checkout when maybe it should be doing something else - but I don't know what!
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I'm hoping that this would be quite a simple job for somebody with a knowledge of drupal module programming - which I am not!