First and foremost the lockstrip MUST be on the OUTSIDE!!! The video showing the lockstrip on the inside is WRONG. The seal is designed to seal with the lockstip on the outside, I have helped many owners who their windows
either leak or in a number of cases have acutally blown out while driving on the highway all had the seal installed backwards. The seal is not strong enough nor designed to be installed installed backwards and you risk major problems. I also recommend that you use a new seal, the original is probably getting hard and will not only be difficult to work with but it will probably leak after you go to all the work of replacing the window.
If you want a cleaner look use a one piece locking seal rather than the original two piece .
This is a one piece seal installed the correct way with the lock on the outside
The following info and more is on my website Boler Front & Rear Windows
When replacing the windows
the rubber molding is first placed around the opening, I like to start on the top, holding the molding in the center (so you have 6′ on each side of your hand) and start working the molding over the fiberglass lip. As you progress use a rubber mallet to pound the seal onto the body making sure it is fully seated. Work the molding around the corners, again using the rubber mallet to make sure it is fully seated THIS IS CRITICAL!!. Continue working your way around, alternating side to side. When you reach the bottom trim one end so it will be in the middle of the opening and seat that side. Take the final side mark the end so you have the 3/4″ overlap, glue the two ends together then seat the final section. Finally go around the molding one more time with the mallet making sure it is fully seated, then you are ready to start the window install. The best tool to cut the molding is a pair of garden pruning shears.
Mix up a soapy water solution and generously apply around the molding and window edges, place the window in the lower groove then slowly work the molding lip over the edge of the window. Be careful not to scratch the acrylic, I made simple plastic tools for this out of some scrap acrylic. They look like a letter opener with a slightly rounded point and beveled edges to a rounded edge (don’t need anything sharp).
Continue pressing the window into the molding while at the same time gently prying the molding over the glass, also continued to apply more soapy water, I used a spray bottle, applying every minute or so. The job is not hard but it can be frustrating at times as the window may want to pop out at times, an extra set of hands is useful. the final little section the window will “pop” into place.
You’re not finished yet, now the lock strip or the locking tab depending if you used one or two piece molding. Continue to use lots of soapy water and work the seal into place, special tools are available to install the locks, but I find various sized blade screwdrivers (preferably ones that you have eased the sharp corners). Again work your way around the window, gently spreading the molding, pushing on the lock until it slowly snaps into position all the way around.