Has anybody replaced theirs? Mines a bit gnarled up but can't find any replacements advertised on eBay.

Mk3 by the way although not sure it makes any odds.

Hiya buddy
i'm lead to believe ( right or wrong ) that the mk2 & mk3 are more or less the same engine and i'm sure they share the same 12mm sump bolt ( hopefully some will confirm this or correct me ).
mk2 part number 92800-12000
heres a handy little link found on this forum that gives you ( expensive ) alternatives as well as the original
http://www.cmsnl.com/search/partnumber. ... modelcode=
For parts for my R1 and for getting prices in general i use fowlers
https://www.fowlersparts.co.uk/search/part/92800-12000

Or you could try Tom at Leisure Trail and he'll know for definite if they're the same part , on a bunch of parts i found Leisure Trail slightly cheaper than both fowlers & David Silvers
good luck