the way I found out was as follows
go to
https://www.bosch-home.co.uk/customer-service/care-protection-and-parts/spare-parts
put in the Enr number ( like WAN28050GB)
the site then give you a list of machine with this number. unless you have looked at the machine in person you will not have the last 2 digits so chose the highest number.
this will bring up the parts diagrams for the machine. scroll through the diagrams to find the drum. Look at the pictures of the drum parts. check 2 or 3 of then like inner drum, drum front half and drum rear half. if they are different part numbers and prices then the drum is not sealed
Dave