Add softened butter and oil, mix on medium speed until totally incorporated and crumbly.
Add milk and 4 eggs, one at a time. Mix until everything is well-incorporated.
Add rum and vanilla, mix one more time.
Pour mixture into bundt pan sprayed with non-stick spray.
Bake at 325º for 50-60 minutes or until toothpick inserted in center comes out clean.
Take cake out of the oven but leave it in bundt pan and set aside to make the sauce.
For the syrup
Add all ingredients for syrup EXCEPT vanilla in sauce pan. Bring to rapid boil and then reduce heat to simmer.
Simmer mixture for 5 to 8 minutes.
Remove from heat and add vanilla.
Poke holes all over cake with skewer or chopstick. Spoon out syrup all over cake slowly, allowing it to soak in completely. Continue adding syrup until it has all been poured over the cake.
Leave cake in bundt pan until it has cooled down to room temperature then invert cake onto serving plate.
Once cake has COMPLETELY COOLED, cut and serve. Enjoy!