Getting back to the OP's question:-
SoGA requires new products sold must be free from defects. If a tyre has been repaired it means it must have been faulty at some point in its past life.
If the dealer knew or had reasonable means to establish the condition of the tyres on a new caravan they should not sell tyres with a puncture or a repair on a new caravan.
You should tell you dealer about this as it should concern them, but I'm not sure what it is likely to achieve in this case, Bear in mind that its two years since you had the caravan, and the even though the tyre was repaired, you did not know it to be so and it has not prevented the caravan from being used safely and normally.
Even when you purchased the caravan you had known the tyre had been repaired and you insisted on having it replaced (which is of course your right) you could have suffered a puncture on the road coming away from the dealership which you would have had repaired, and presumably used the caravan without a second thought. So have you suffered a loss of function or value in real terms ? I think the answer is no.
Now I am not condoning the practice of selling repaired tyres as new. Far from it, but I think there has to be a sense of realism here. Whilst you are certain you have not had the tyre repaired, and that is why you believe the tyre was repaired before you purchased it, you problem may be proving that to be the case.
As you have not suffered a loss as a result of the repair what is there to be gained by pursuing a case of which there is no certainty of success.
Even if you were successful what would be fair remedy? The tyre is now two years old from purchase, so a new tyre is not a fair option, The tyre has already been repaired apparently successfully so no further repair is called for. So all that is left is compensation. The only loss you have suffered is the difference in value at the time between a brand new tyre and the value of the repaired tyre, Who can value a repaired tyre?
I have to say there are several different points in the supply chain where the tyre could have collected a puncture and a repair made, of which the dealer may genuinely have no knowledge of its occurrence. Even though the dealer may be innocent of having the repair carried out, SoGA makes it very clear that the seller is legally responsible for defects in goods they sell.
I think telling the dealer of the issue is necessary (because they need to be aware of the issue and the fact it has been detected all be it 2 years on) But bearing in mind the facts of the case as presented here, and unless this forms part of a larger issue with the dealer, in my opinion, demanding some form of compensation is going to muddy the water. Hopefully and assuming the dealer is basically honest, they could offer some goodwill gesture of some sort, perhaps money off a service, or a discount on a purchase from their shop.
As consumers we do need to vigilant, and dealers need to understand the legal responsibilities they have when selling goods, and the buying public is becoming increasingly savvy about their statutory rights and how to use them.