There should be a seal between your pipe and the silencer. Let us know what kind of bike you have. On average, a 125 likes 32:1 and a BR9EG plug. A 250 likes 40:1 and a BR8EG plug.
No disrepect to the previous owner, but you should verify the bikes condition for yourself. Spooge can be a sign of; a leaking crank seal, improper fuel/oil ratio, wrong heat range for your plug, dirty air filter, bad rings, ect....
Clean your air filter, make sure you have the correct and new plug, mix a fresh batch of gas/oil, and start jetting. Don't forget a compression check and a silencer repack too.
Good luck, Steve.
Stock jetting seems a bit rich to most, here is a site to give you a base line;
http://www.mx-stuff.com/jettingspecs.htm
A few good sites about jetting;
http://ericgorr.com/techarticles/carbtuning.html
http://justkdx.dirtrider.net/carbtuning.html
http://www.teamgreennews.ca/techside.html#carbjetting
http://www.teamgreennews.ca/techside.html
http://www.thumperfaq.com/mxa_jetting.htm