Aero bars moving...!

Hi all

Slight problem I would like some opinions on please.

I have a set of HED aero bars (can't post an image at the moment, but if you search for HED AEROBARS in google images it is the first few pictures that appear), they are a few years old and are not 'oversize'. I needed a shorter stem and could only find what I wanted in the more modern 'oversize' bar size. Not a problem as I bought a set of alloy shims to convert oversize to the older size. Am I making sense?!?

I have fitted them and set the bars up....much better reach for me and the whole ride is transformed. Happy bunny thus far. However, a problem has arisen when I hit a pothole whilst on the extensions, the jolt has caused the bars to shift downover. Quite a moment arm I suppose with elbows in the pads and hands on the extensions.

I am a little worried about tightening them any more and wondered if anyone had come across such a problem and how they had got around it?

The way I see it is the bars are carbon, the shims almost polished alloy and therefore very smooth. Would perhaps carbon jointing paste be a good idea to cause a little more grippy ness? You know, the stuff they use on carbon seat posts?

Thanks in advance

PP