Sounds like a main oil seal. If you have the engine steam cleaned and then inspect for the leak afterwards you should be able to see the exact spot that the oil is "gushing" from. You have ruled out the two obvious places that oil can "gush" from ( drain plug and filter) and when gaskets like what you find around the oil pan and rocker covers (or valve covers) leak they seldom "gush" and tend to "weep" oil. That leads me to believe that either the front or rear oil seal has failed which would definitely cause a "gush". Although an oil seal is not an expensive part, the repair is quite involved and labor cost would be high.

There are different grades of Loc-tite™ Thread locker available. Red high strength, Blue medium etc. Normally you apply a small amount to each part before assembly. Also there is a penetrating grade that you apply after assembly. Be careful not to get any of the product on plastic parts or the finish of your axe as certain plastics will be damaged. I have used teflon tape to prevent dart shafts from coming loose from the barrels and many players use small "O" rings which compress and work much like a lock washer does keeping tension between the shaft and barrel. As a last solution you can try turning your amp down!! ; ) Rok n Roll!