My bikeīs stem and handlebar have non-matching diameters. The handlebar (a Nitto B135) is 25,4, the stem (Shimano Ultegra) is 26mm. This all happened because of an ebay seller failing to properly list the stemīs specs. But I want to keep it, for one it is beautyful, and more importantly it is short (80mm, not easy to find plus it would probably cost me more than the 40€ I gave for the Shimano), something I need as the bike itself is a bit long for me.

First I tried with a beer can, then I bought a VO handlebar shim and tightened the bolt as hard as I could but given enought time the whole system will still loosen.

I was wondering if some assembly paste would help me keeping everything in place or is my only option getting a 26mm handlebar?