I fixed the leak at the flare, moved to Nyloseal and did another leak test with a digital meter.
The leak at the flare was an easy fix: just tighten the b-nut a bit further.
Although I torqued this to the right value during installation, but what I did wrong was torquing the fitting instead of the b-nut because I didn’t had a crowfoot. This probably resulted in a lower effective torque due to the higher friction.
After some discussion on the Sling Builders Facebook group I considered Nyloseal fittings. The push-in fittings from SteinAir didn’t leak but since the pitot tube is in the wing and there is only a small inspection panel that allows only one hand to go into; so the tubes should be removable with one hand. With the push-in fittings this is difficult, Nyloseals are more practical here.
I did another leak test, for this I purchased a digital meter (Testo 510i) that sends the values to a smart phone or tablet:
It has a leak test program which is very handy for testing the pitot tube.
It’s difficult to seal all holes (pitot, aoa, drains) of the pitot tube but I tried several ways but although nothing was leaking I still had more than 10 kts pressure loss in 1 minute!
I removed the pitot and tested only the pitot and found out that the “leak” is in the pitot itself.
That’s al lot more than 10 kts / mininute in AC43-13-1B. I sent an e-mail to Garmin and they proposed to replace the pitot tube; great service! I returned the pitot tube via a Garmin aviaton dealer.
Let’s wait for the new pitot tube…