Like the title says. The xj has a very very soft pedal and it pulls hard left. Should I flush the system and replace everything?

 

Pulls hard left while braking? I'd start by noggin pokin. Easier for you to find the problem since you have access to the vehicle, harder to take a wild guess online. Maybe "everything" needs to be replaced, might just be leaking from one spot. When's the last time you inspected your brakes? Is the fluid low?
Soft relative to what? Softer than it has been? Softer than a Porsche brake feel? Is the vehicle new to you?

 

Its a xj I am thinking about buying. Its softer then any other xj I have ever driven. Would a leak in the line cause a pull? Oh and yes it pulls when the brakes are engaged

 

I'd say do the best visual inspection you can, and weigh what you see (or feel) against the price. Could be many things causing the pull, same as the soft feel. Many things but usually somewhat simple to sort out and fix.

 

Pulling to one side when braking I would lean towards a frozen/stuck caliper more than a leak. That will also cause soft brakes. You would be able to tell pretty easily by pulling the wheels and calipers off, the pads will be worn all weird and the slide pin(s) probably won't move much if at all.

It doesn't cost that much to R&R the whole brake system, the hard lines are the biggest pain. A leak would be pretty obvious, you would find wet spots were the leak is.

 

Best way to check for a frozen caliper IME is to drive it for a while and then feel the wheels. If the brakes are making contact when they're not supposed to, the wheel will be hot.

 

Soft pedal can be air in system, old rubber brake hoses, break-booster issue, leak in master cylinder. Or, as in my case: no cause found.

The pulling to one side (only when applied the brakes), would more point towards a failing caliper on the opposite side.
If the pulling towards one side occurs at all times, then a stuck caliper on that side could be the case and most likely also give increased temperature.