Pressure Law gas leak

I tried to do the Pressure Law experiment. It hadn't worked the year before and I worried that the range of temperatures wasn't high enough to produce a convincing and measurable rise in pressure. The scale divisions are every 20 kPa (red scale - see below)

Normal atmospheric pressure is just over 100 kPa at say 25 degrees Celsius lab temperature. I used boiling water to raise the temperature of the air inside the flask to 100 degrees Celsius. We waited long enough to allow there to be equilibrium between the water and the air temperature. p1/T1 = p2/T2 gives 100/298 = p2/373 as the temperatures have to be given in Kelvin. The higher pressure will be 125 kPa so over a (wide) scale division higher. It would be measurable. But the needle didn't move. There must be a gas leak causing equalisation to atmopsheric pressure (ie it's not a closed system). So this week I tried sealing the gaps with Vaseline which worked for half a minute and then the leak returned.