When on the 2008k the condo cal takes forever or does not cal properly which condo cell do you change?

I'd probably start somewhere other than the condo cell. They very rarely go bad. Flow pressures, sensor bd. and function bd. are the more likely candidates. If you want to try changing the condo cell, it would be the pre condo cell, the one closest to the balancing chamber.

Did you have a problem with conductivity and are you trying to solve it by calibrating the cells? Either way I would check my acid and bic pumps/rates first before changing a cell.

I have seen flow problems cause problems with the cond. cal. I'm not talking about big flow problems like flow alarms, or no flow at all. Watch the flow indicator and see if if rises and falls with the same precision as a good machine.

If flow is just a little bit "unstable," the cond. cal will never "lock in." With old machines, I have seen very worn-out, thin balancing chamber membranes be the problem: they do not have to tear to cause mild flow problems (which in turn affects conductivity).

do a conductivity cell calibration, and WATCH the conductivity value while "waiting until stable." If that number fluctuates too much, it is possibly some sort of mild flow problem, whatever the cause. If necessary, watch a good machine cond. calibration to see what "stable" should look like.