The internal slave cylinders are acutally less cool than it might seem, not to mention of inherently weak design. I had to change one this summer in the middle of one of our heat waves. Got it all torn down and found a date stamp on the old Slave that indicated March of 2008. So it couldnt have possibly been in there more than an year and a half or so. So I installed the slave I got from advance, put it all back together, bled it and drove it ten miles before the slave started leaking again. So I ordered the ford part, and had it installed the next day after which the also brand-new-from-autozone master cylinder ceased to pump within 24 hours. Ordered the ford M/c and a new clutch line, because why not? Now I have a totally new clutch system.
Two big lessons here:
For internal slave cylinders, OEM parts only. Pulling the trans is enough work to justify the cost as long as I dont have to do it again for a while.
Manuals may not be that much less expensive to maintain than Autos (If taken care of).
I say all that to say this, I considered bolting up the 4 speed I have behind the house so I could have the external slave. Plus I can R&R a t18 by myself...