You don't have to take the fender off but it is replaced from underneath the car. Lift the car up on car jacks or ramp. Make sure the ignition is off. Pull the reservoir fill pipe off...pull hard, it will come loose. Remove the level sensor connector and pump, and washer reservoir screws. Then you can remove the reservoir. Next, remove the hoses, and the level sensor by pulling upward. Remove the windshield washer pump by pulling from under the car (it's in an indentation on the side of the tank), and the tailgate washer pump by pulling upward through middle of the tank's indention (should be obvious). Now that you have all the components loose you should be able to take the tank completely out, and either see where there's a crack, or pressure test it for a leak. You can repair these with some epoxy and avoid buying a new one, or if you want, you can buy one for $40 at http://www.fcpgroton.com/volvo850wiperwasher.htm Reinstall all parts in order they came out and you're good to go.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.