Which engine to replace a Volvo MD2020 in a Beneteau 311

[Excakibur311]

My Beneteau 311 is a 2002 boat that I have owned for 12 months, towards the end of last year I started having issues with the MS10L-A gearbox not always engaging drive, either ahead or astern which has led to some very stressful moments in various marinas, this seems to be almost exclusively when the engine and gearbox are cold. Secondly last weekend the engine dumped its coolant into the bilge via the pressure relief valve on the heat exchanger, which I understand is most likely a blocked exhaust elbow.
Im finding it difficult to find someone who can rebuild the gearbox its casing's indicate its a Hurth gearbox but I'm told Volvo make small changes inside making the Hurth specialists reluctant to touch it.
Given these two faults Im wondering if it isn't time to replace the engine and gearbox, hence the question what with?
Has anyone on these forums replaced the MD2020 on a Beneteau 311?
Can anyone who has had such a gearbox rebuilt direct me to a suitable repair company?
Any recommendations for a brand of 20HP marine diesel and an installation team?
The boat is moored on the river Hamble.

Many Thanks

 

[Tranona]

Simplest and most straightforward replacement is the current Volvo D1 20. Less than a day's work, no modifications to the boat nor change in propeller. You should be able to get a good part exchange deal from a local Volvo dealer such as RK Marine or Golden Arrow. Alternatively a popular replacement engine is a Beta, local installer TS marine. Other suitable engines are available from Yanmar (which are fitted to many Beneteau models) Nanni or Vetus.

In terms of reliability, life, refinement etc there is not much difference, and cost will probably not vary hugely (it is a very competitive market). There is something to be said for sticking to the original make - and Volvo come with a longer guarantee period. However your choice so plenty of suppliers to get quotes from.