I have a theory...

If any of you guys own modern Tissots, you know that most of them have a press-on caseback with an unusual red plastic gasket instead of a typical rubber one. Though Tissot is one of my three favorite brands, the gaskets/casebacks they use have always bugged me because they aren't user-friendly; the fact that you have to absolutely ruin your caseback in order to open it, in conjunction with a proprietary gasket and non-standard method of regulation with Powermatic models, makes the timepieces of the best affordable Swiss watch brand ironically very unfriendly with tinkerers and independent watchmakers alike.

But I have a theory as to why Tissot uses plastic gaskets as opposed to traditional ones. While it does allow them to have further control over servicing and parts, I personally feel Tissot is onto something, even though the advancement they introduced is pretty minor and a little annoying.

As we know, rubber gaskets, especially those found in watches with higher water resistance, require some care and semi-regular maintenance in order to keep water out of the watch. You have to make sure they're still pliable and/or "fresh" in order for them to do their job properly (which entails using silicone grease and replacing the gaskets every few years in order to maintain your watch's WR). Regardless of what you do though, there will come a time where you'll need a new gasket for your watch but it'll be a PITA to find a generic one.

I think Tissot’s logic behind their modern gaskets stems from the cost/ease of servicing. Because Tissot is basically the Seiko of Switzerland (due to their history of mass producing quality timepieces) they make, and therefore have to eventually service, millions of watches a year. Although it would cost them basically nothing to use rubber gaskets, I think Tissot uses them in order to reduce the amount of times they have to be changed. Because they're made of semi-hard plastic and not rubber, it's logical to assume that a lot of the challenges rubber gaskets face-being susceptible to hot and moist climates and losing pliability over time, for instance-are at least partially negated. I could imagine that as long as the gasket is in good shape and the seal between the caseback and case is tight enough, an average plastic gasket could last far longer than an equivalent rubber one, even with maintenance. And although it's cynical, it allows Tissot to have further control over servicing and repairs.