Complex sentence: The main maintenance depot was at Birkenhead North, dedicated to the units, where careful attention allowed them to remain in good condition right up to their final withdrawal in 1985, unlike some other units elsewhere in the country at this time.
Split into simpler sentences: The main maintenance depot was at Birkenhead North, dedicated to the units. Careful attention allowed them to remain in good condition right up to their final withdrawal in 1985, unlike some other units elsewhere in the country at this time.