When I come across thick old oil like this, I’ve found heating up the gearcase with a heat gun loosens it up so it will flow out better. Then letting the motor idle in neutral for a few minutes with 10W 30 or whatever motor oil is available before draining it again will help remove whatever is left of the old stuff before refilling with the correct gear oil.
Ii would loved to have seen the look on these anglers faces when they thought they had hooked the big one years ago!
