Regarding Rear Axle Lubricants mentioned above . I queried the factory about the preferred lubricants back in 2009 their reply is below:-
Dear Mr Smith,
Your car is a 1999, which would mean that the axle in your Plus 8 is a BTR. The lubricant recommended for this axle can be Castrol SAF-XA, or Mobil SHC80w-140ID. These are the recommended lubricants for this axle.
At the Morgan Motor Company we currently use Morris’ oil lubricants and we use an 80/140 synthetic, which is known XFS 80/140. We have used this for many years now. It also contains the additive to which these axles need. Our recommended interval for change is 100,000 miles or 6 years, whichever comes first.
We hope this answers your question, but please feel free to come back to us of you have any other queries,