Tiller gearbox

I was tilling away for about a half hour until a volcano of boiling yellow and green goo erupted from rubber plug. Will the entire gear box need to be stripped and cleaned. Any ideas what would have caused this. The unit was bought new by a relative, used for a very small project, and sat in storage for four years. I picked it up last fall, changed the motor oil, cleaned the carb, and observed the gear case was at the full mark.

Water in it would be my guess.

Clean it

water in the oil. Then a bearing got hot because water is not a great lubricant. When the bearing got hot on its way out, the water got to boiling point and thats when ya end up with a mess like that.

Thanks for the replies.

Now don't just clean it up and fill it with oil. Strip it down and find that bearing that is running hot before it starts spitting teeth or disassemble itself