Hi henri
Ian commented on a similar problem recently, have a look at:
http://pub37.bravenet.com/forum/static/show.php?usernum=3155626639&frmid=16&msgid=1241302&cmd=show
I don't know how essential the oil groove is but as many that I have seen (other bikes) don't have it I guess it's not that critical
. I now expect to be shot down in flames! 
Cheers
Pete
email (option): petercomley@web.de
hi henri,there is a couple of ways to fix the problem of a loose bush.
1 )if the fit is good on the pin make a couple of cones in your lathe with a hole through and put a bolt through ,tighten up and expand the ends of the bush into
the con rod, this will only create a small chamfer at the extremes of the bush.
2)if you are competent with your lathe,the oil groove is exactly that,no big deal
just a course screw thread through the bore.you will have to set your change wheels to create a pitch of about 1/2'' to get a double spiral over the distance of the bush,drill your oil hole at the centre of the groove and fit that to the top.alternatively put a groove about 1/8'' in from each end of the bush,then turn your boring bar sideways and join the two grooves up with a horizontal slot by just hand feeding the saddle from one groove to another,drill the oil hole into
this groove and all will be good.sounds daunting written down but really is straight forward.
if you can get the pitch for the groove and your lathe is a bit fast,pull the chuck round by hand using the chuck key,leave the screwcutting engaged until you have got the required depth.
hope this helps,cheers rick
email (option): richardholt@rocketmail.com