I had this issue on my GTV in the late 90's.
I had a flat so used the banana milkshake solution and compressor and worked a treat.
Took it to the tyre shop and they said they would only sell me a new tyre because of the mess. I insisted on having a look and found that there was next to nothing in side the tyre. The solution does not foam it stays runny and when it finds the hole, it cures, same as radweld really. I said there is nothing to clean up!
They then showed me the tyre wall and said they cant repair is because the sidewall had split...tiny little stress markes, so I agreed to it.
They then ordered a new tyre and had it shipped down that day so I walked off to work.
Got the call, went to pick up my car to be presented with a bill for £350!!!
On closer inspection, they had tried to charge me for a pair of tyres, only fitting 1, oh, so sorry sir, we will get that sorted for you. So I then get a bill for £175 for a Goodyear F1 17.45.225 tyre which I could of got anywhere for under £100 fitted.
Basically, dont trust a random tyre shop. I use the same tyre shop, build up a rapor with them, let them know you know what you are talking about.