Inspecting mbuf contents (was: mbuf cluster leak)

I'm again being hit by what appears to be an mbuf leak.
Triggered by reasons unknown, on our gateway, mbuf cluster cache usage starts 
to suddenly ramp up up to the point the network ceases to work.
Only a re-boot helps.

All of the mbufs are allocated to tx of a certain vlan interface.

So:
> I'm still wondering whether there's a way of inspecting the contents 
> of those mbuf clusters. I strongly suspect that looking at the contents 
> will give a strong hint at what's going on.
any way, to, on a live system (as soon as it starts to ramp) inspect those 
mbufs to get a hint on what the leak is related to?