Only just read this thread, its certainly interesting.
To the OP, beware of just whacking on a piston and pot as has been suggested. Unless you find the cause of the failure beyond any doubt then you risk a repeat of the problem.
Can pistons and pots be changed in 15 minutes? Anything is possible I suppose but do not take this as the norm. I have certainly never got anywhere near that time, and all machines are different.
Stihl, for example publish their repair times for all tasks. A P&P, inc pressure test, on am MS181 takes 120minutes, on 200T 60 minutes is allowed, whilst a 361 is given only 45 minutes.
But these times are set by the factory on brand new saws. The diagnosis and cleaning prior to the work will take at least another hour on a saw in 'used' condition.
And, is it worth trying to save a piston? In my opinion NO. But thats because, at dealer rates of around £50 per hour it will cost £300 in labour given Spuds realistic 6hr time scale. Add the parts cost to this and it easy to see why saws are so easily written off at a dealer. Far better IMO to fit a new (OE P&P)
Fair enough for this written off saw to then be resurrected by someone of Spuds skills and labour rates.
But as Spud says, the job does not stop with the P&P. A good technician is inevitable going to spot other issues that need fixing, or at the least they need to be pointed out to the customer. We would of course, prefer to fix all faults before returning the machine to avoid it being returned shortly.
Also, as others have said, keep clear of aftermarket pots and pistons in general. If you are fitting it yourself and not costing your labour, or if you have a Billy Whiz doing it for 15 minutes pay, then it may be worth the risk, as you wont have much to lose.
Hire shops fit aftermarket pots as they know that there is a reasonable chance that the machine will be incorrectly fuelled, so why trash another OE unit?
Just trying to show the whole thing from another perspective.