Yep, I've the L series, in fact 2 of them. One is now on 182000 miles and still going strong. I took mine to MG-Rover Mobile Mechanics at Derby as I wasn't sure where it was leaking from, but they soon diagnosed PAS pump and proceeded to change it. It's not the easiest to get to, but I think matters are simplified if you remove the splash guard, and support the weight of the engine on a trolley jack. Undo the top engine mount on the drivers side, and raise/lower the engine as required using the jack.
New PAS pump was £120, (with £100 exchange surcharge on the old one), they are factory sealed, so if the leak is on the dividing gasket, replacement is the only option. May have said before though, check the union on the feed from the reservoir first, (from memory I think there's a copper washer top and bottom that makes the seal), apparently this is a common leak point.
You really don't want to be undoing the air con unless you know exactly what you're doing, it's illegal to discharge the gas into the atmosphere and can cause nasty chemical burns if you get too close. May find for a £45 recharge it works too!
If you use Facebook, why not join the MG-Rover Diesel Owners Club, always a wealth of advice available.