After a lot of tweaking OLSR running on Linksys has had no "ping down" messages for about 5 days now. Some of the tips to getting OLSR on OpenWRT stable.
1. Lock all the nodes to 802.11B don't let it auto sense
2. If there are any v2.2 hardware devices, change the clock speed to 216MHz with the following commands1
# nvram set clkfreq=216
# nvram commit
3. Lock the RX and TX antenna to the one you connected your external antenna too, don't use AUTO. TAKE NOTE!!! On Version 2.0 hardware Antenna A is on the left looking from the front of the linksys and and on Version 2.,2 hardware Antenna A is on the right looking from the fron of the linksys. This caught me out a few times.