Hi, I have a slow air leak in one of my tyres. I am losing about 5 psi in about 4-5 days.

I dont think its an actual puncture and i believe the air could be leaking from the side wall.

Is there any tyre sealant which i can use to stop the air leaking out?

Try spraying water/soap around the tyre and look for where it’s bubbling, that’ll confirm where the leak is then.

Best find out if a nail in the tyre or damage.

Just today i put Tyre Weld in someones wheel that leaks air even after they have had the tyre refitted a couple of times and sealed at a Tyre Fitting Centre.

It works well enough with leaky rims.

I've had a look and there doesn't seem to be a nail in the tyre....

I would suggest removing wheel and with it laid flat spray soapy water all over it paying special attention to thr beads as its not unknown for corrosion to develop on the alloys where the tyre seals causing  a  slow leak , it will also be easier to examine the rest of the tyre off the car.

The last 2 siimilar leaks I had were due to faulty tyre valves and occurred some time after tyre replacements.

On a mkII, i'd say corroded valve seat / seal.

 

It was on mine............Ask the next fitter to check this for you, and thoroughly clean / file off if necessary.

 If you use a sealant, i believe this makes it very difficult for fitters, they may be reluctant to work on it. and it may not work anyway if corroded inside. 

Check around the valves I had the same problem.

Deffo another vote for valves and corrosion causing the leaks. Had this on both my front tyres. It was much improved when the fitters tried a bit harder to clean around that area before fitting the new tyre and valve.