Evinrude remote Control, Gearbox problem Engine from 1974

I have the problem that makes our age-old (1969) Almar 16 foot boat with the hitherto superb running AB Evinrude 135PS Type 135483B, 4-cylinder, 2-stroke from 1974 difficulties.
We use the boat exclusively for water skiing.
The difficulties initially expressed themselves over too low idling. The engine died when going in gear.
Unfortunately, we have always increased the speed by using the cold start rotation lever on the remote control. (Not choke)
At first, at full speed, there were blows from the engine with little thrust loss at undefined times. These piled up then. First guesses were dropouts of the ignition or even the fuel supply. (sealing LEAF PLATE in the intake channel)
But the last ride ended with a boat that was no longer moving forward. The throttle / gear lever could be moved forward the forward gear was engaged but then jumped out immediately and with a "vibrating" throttle / lever.
Driving was only possible backwards.
The remote control I have disassembled and can find little wear or damage.
Now the question:
I have it possible that the transmission (jaw clutch, shifter, clutch dog) has survived and only the circuit needs to be adjusted?
Does anyone know about these antique things?
Please excuse my English!

Drain the gear oil first.----Look for metal bits in it.-----And do a compression test before spending any money on it.

Sounds like major issues in lower unit. Yep, look for evidence.
There is no way the control can hold it in gear if the dog and forward gear are worn out.

We are very familiar with that motor and lower unit.----But you have to do the work and inspections.

Nothing real special other than its the hydro mechanical gearbox if you dont see metal shavings in the gearoil do a reseal it could just gunked up from old or incorrect gearoil. It takes type C gearoil?

Type C is not needed for that lower unit.-----Use oil called ----Hy-Vis----in that unit.

Thank you for your quick reply.


There were more spikes on the gearbox drain plug than on the other oil changes. But if that was "too much" I do not know.


I regularly change the oil.
I use HI-VIS gear oil.

That could be wrong, of course.At the time there was probably a change in the oils to be used.

Hi-VIS is the correct oil !!

I just assumed all hydro shift gearboxes used type C. You definately need to open it up and give it a eyeball.

Can you tell me if there is a gearbox gasket kit for this engine?
Unfortunately, I can only find the gasket set for newer engines.
Or can someone tell me which seals I have to order.
I finally got the retainer out. The lower unit is now dismantled. I change the forward gear and the claw clutch. What else should I exchange for safety? the oil pump?
or something else?