Wrong gear oil in hydroelectric lower unit

[69StarcraftJupiter]

Hello, I have a new to me 1970 60hp johnson outboard with hydro electric shift. I just got the boat an it seems as though the previous owner was using standard 80w90 gear oil instead of the manufacturers recommended type c.
When I bought it the guy fired it up for me and ran it in Fwd and Rev to show me it shifted fine. My question is, how should I go about flushing the lower unit of the old 80w90 to replace it with type c?
Should I just dump and replace it and run it like that or is it recommended to take it apart and clean it out before replacing it?
I figured if it's running with the 80w90 than it should be alright to just replace and move on but I'm interested in what the group has to say.
Thanks for the help.

 

[69StarcraftJupiter]

View attachment IMG_20210322_160641.jpg

 

[racerone]

Let the oil drain for 2 days.----Then fill with TYPE-C for electric shift ( BRP PREMIUM BLEND ) and enjoy that fine electric shift motor.----No damage was done by the 80W90 gear oil.

 

[69StarcraftJupiter]

Let the oil drain for 2 days.----Then fill with TYPE-C for electric shift ( BRP PREMIUM BLEND ) and enjoy that fine electric shift motor.----No damage was done by the 80W90 gear oil.

Thank you. That puts my mind at ease and a smile on my face. Have a great evening.

 

[oldboat1]

If you want to be extra cautious, drain the unit and refill it with ATF. Run it just a bit with the ATF to heat the oil up a little, then drain it and refill with the considerably more expensive Premium Blend.