So i have a 25hp Johnson and the gears are locked up. the motor is in neutral and the prop wont move. the motor won't change gears and the flywheel also wont move. last time we went out it ran fine, got it out of the water and started driving home. I did hit a bump really hard but idk if that could cause this. I have no idea when the last time it was serviced and I have had it for 2 seasons now, and I have not done anything to it either. I do believe there might be a bad seal being that some oil leaks every one in a while but its not discolored in any way. But I just need help on how to fix it and get it ready to go by this weekend.

Drain all the water out the L/U.

With it leaking have you ever thought about fixing it and putting fresh oil in it. If oil is leaking out then water is getting in.

I think it will be toast.

Drop the lower unit to see if the flywheel will turn. if it does then you know its the lower unit. If not then you know its the top end. I bet with the temp it has been and that you live in Wisc and more than likely have water in the lower unit. Its frozen up. Drain that lower unit. put a new seal in and then use synthetic oil in the lower unit.
You probably have the water/oil sludge mixture.
Put you a new water pump on it while your at it.

1. does the shifter move, forward, neutral, rewind?

a. shifter moves - still locked up - lower unit, clutch dogs or froze water in LU

b. shifter doesn't move - possible froze or bent/disconnected linkage

2. Put rig in garage with heater on motor and drain lower unit

a. water in LU unit, replace seals as stated earlier

b. no water in LU, remove LU and determine what is locked up - motor, lower unit.

Either way you should be replacing water pump at least every other year. Especially if rig is used for waterfowl hunting or other shallow water activities

You can order from here but if you had straight water in the gear case I'm afraid you'r going to need more than a seal. Good luck.