As above old seal will be damaged in removal as they are a interference fit so hard to get out if you don't have a seal puller.
If the slave cylinder has gone it's a box off gone as the F23 doesn't have a inspection plate like the older F20 gearboxes did.
It's worth checking that the O ring isn't damaged on the top plastic part that sticks out of the gearbox where the alloy bleed unit is pushed onto and the clip put in.
When my slave cylinder went it started slowly on initial start up not coming out of reverse or sticking in first so had to turn car off pump it a few times and then re start car. Did you have anything like this?
