Drilling the slave cylinder is to let you know that the seal is on the way out (not a common fault from what I can see but it has happened) so that remedial action can be taken before a new clutch plate is needed due to oil ruining it.
If I ever get around to getting my 1100 back on the road then this is on my list of jobs to do. The more I read about this stuff the more I worry. Ignorance is bliss!
All the info is on several relevant threads on Pelican. The guys there seem to think it’s a good idea so why not! At best it may stop you going on a long journey/holiday and then having a problem you could’ve known about before you set off?