No the E28 is an easy one to replace. Yes and no on the gasket replacement. If its still soft and pliable with no damage its a keeper. You may want to look into replacement gasket lock/trim and might want to invest in some M5 type black trim its spendy but well worth it since the original stuff can look pretty bad and it also shrinks a little. A HUGE mistake window guys make is using sealer. A good gasket and a good install job can easily keep a water tight seal. Another mistake is guys tend to use tools like picks and screwdrivers when installing to manipulate the gasket causing small scrapes to the paint and sooner or later there is rust and then a leak. Its important to watch the guys and step up and object to whatever you see being done right. Also when the old window and gasket is out inspect the area well for paint damage and rust. Also the interior trim is glued onto the body in the gasket area and with time the glue likes to get go and then the window guy going for looks and not quality try to hide this by stuffing it under the seal improperly. If the guys insist on using sealant walk away its nothing but a problem down the line.