Found the following extract on the Hanse forum which offers a suggestion of costings, sounds expensive.

    Posted: 09 February 2009 at 20:06
    Well. I’ve just done this job on my (just) 7 yr old 301 so it may be worth sharing my experiences.

    It says quite clearly in the Volvo Handbook that this should be replaced every 7 years, which is the only motivation for replacing it. After speaking to my insurer (Bishop Skinner), they said that if I didn’t replace it, and there was a claim that in any way involved anything related to the area of the seal, then it is highly likely the underwriter would take the opportunity to avoid paying out. Due to this likely being a large sum (i.e. total loss) I was not prepared to take the risk. Dealers quoted £1300 labour (assuming 1 day) and parts (presumably at full list price) plus additional cranage (refused to work in my marina for political reasons meaning re-assembling the now dismantled engine covers etc) at their own yard (which wouldn’t take the fin keel draft in any case). This equals circa £2000, so not an attractive or indeed economically viable option.