Also remember to set the left locator at the dropin point then enable dropin on left locater.
Here's how I do it... cut using the scissors around the offending part, make sure it's highlighted, press the P key, sets the locators to the cut part, press backspace, deletes the offending part, press the I key, sets dropin on left locator then rewind to some time before the drop in. press play, you will hear the old take playing, when Cubase gets to the left locator it will go into record mode and you will now hear yourself playing, if you also have drop out on right locator set Cubase will dropout of record at that point.
Repeat until new part is good.
Sounds a lot but once you get it, it becomes very quick