clutch slave cylinder change on disco 1

The clutch slave cyl has gone on the disco and i've found my spare but have noticed the clutch fork push rod is not part of the cylinder or attached to it.this might seem a stupid question but when i unbolt my old cylinder is there any danger of the rod falling into the box or is that not possible?

You need to carefully remove the old cylinder, and then whilst putting gentle pressure on the rod to keep it in situ use a finger to slide the old rubber cover from the old cylinder that will most likely be lurking in the box near the end of the rod!. There is a small plastic clip keeping it in place. If you pull it out you will have one heck of a game clipping it back in (as i found once before with 2 hours of my life gone that i will never get back!). Dropping the rod into the box will be an engine or gearbox out to remove it! It's not a hard job but just take your time.

Thanks for that,looks like i'll have to be careful (or get sombody else to do it) .also after seeing how cheap new cylinders are i'm wondering if its worth chancing my used spare.

Don't chance a 'used' spare, it will most likely have deteriorated inside if it has been left to dry out. For the sake of £30 fit a new one and the jobs a gud un.