7.34. IP MASQ works fine for a while but then it stops working. A reboot seems to fix this. Why?

I bet you are using IPAUTOFW and/or you have it compiled into the kernel huh?? This is a known problem with IPAUTOFW. It is recommend to NOT even configure IPAUTOFW into the Linux kernel and use IPPORTFW option instead. This is covered with more details in Section 6.7.