I put silicone in my Herald, and later on in my GT6. Although some components were replaced in the process (mainly the pipes), not everything was. It has been 10 years with the Herald and about 6 with the GT6. No issues whatsoever. On the availability question, l just keep a couple of bottles to hand, and one in the car when touring.
Alternatively, I have a TR4A, which has Dot4, and leaked all over the place causing very bad paint damage in the engine compartment and the footwell. It will be changed to Silicone when I get round to it.
Dave
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