It is possible with care to remove the top cover, however, you are working blind for some of the bolt removal / refitting. The important / difficult bit is relocating the selector plate in the slot in the lid Just done this on another car, it's a bit of a pain, slow, but doable. My car has a drain and a top cover filler fitted with a cap / dipstick, fitted by BGH at a previous rebuild, and I can highly recommend both.