I have a 2003 Chevy Truck HD2500 and I have noticed that the rear seal has been leaking, I am sure that there is grease on the break pads, can I replace this or does it have to go into a shop, will it hurt to drive the vehichle.
I'm assuming you mean the piston seal for the rear brake caliper/wheel cylinder? You can change it yourself, but how will depend on which system you have. Instead of me posting procedures for both, let me know if you have drums or discs in the back.
Also, you can drive it, but I wouldn't. I don't know the extent of the damage and/or if the seal/line or something else is failing. If you loose line pressure in the middle of heavy braking, you'll wish you didn't drive it that day.