Well, in my experience the genuine HW ones last a very long time......

One of my 95s.....bought new in 1995. Fitted V-Mach kit in 2014. It was still shooting brilliantly, and very consistently two years ago. So, breech seal about 27 years old!

Conversely, in 2019, a "supposedly genuine HW" one in a 35 lasted two months!

P.S...the 95.....although the seal looked flattened and to be well past its best, it was still quite pliable and, as said, still performed very well.