Water coming in via rear side window

Hi,
When washing my car, I notice that some water got in from one of the left rear side window of my 92 Toyota Windom 3.0G. I checked it and found that the window glass is not pressing as tightly onto the rubber seals. This model does not have window frames on the doors.

Is it difficult to strip the old rubber strips off and replace ? What is a good way to do this myself?

Thanks.