Don't forget all that all new rubber seals are invariably moulded silicone these days. That will be, in effect, what you are doing. Silicone does have it's place in modern plumbing, as long as it is used properly and in the right amounts, just don't use copious amounts everywhere. Just use enough with the clamping plate and old seal as the former to augment the seal and then it isn't a bodge. A bodge would be to smear loads everywhere coating everything, you don't need to do that.