The access hole is in fact just the end of the chassis rail. Be very careful as the chassis is not filed down after being cut, so has some very sharp edges & the rivets used to bond the bits of chassis protrude into the chassis rail and are sharp as, well, nails. You go from underneath, putting your hand up and then through 90 degrees into the chassis rail. If you're under the car, the access starts a few inches behind the point where the rubber water pipe goes into the chassis rail.
Depending on the age of the car, what might have happened is one of these rivets has eaten into the coolant rail itself. However, as I seem to remember it's a sport135 and thus at least a '99 the pipe fitted should be the later type with a kink in it to avoid the rivet
Even so, it might be this that's bust, just less likely (10+ years of corrosion ...).
You'll need a wee 1/4" ratchet with a 6mm socket on it, put your hand up into the end of the chassis rail and feel around to find the clip, put the socket onto the clip's tightening screw and if you're lucky you might get enough room to get 1 or 2 clicks of the ratchet. I'll tell you now, it is just about one of the worst jobs on the S1 elise.
If the coolant rail itself is ruptured, you need to remove the front clam and cut a hole in the crash structure with a hole saw so that you can pull the pipe out the front. This is probably the second worst job in an elise and involves undoing the jubilee clip (see above).
Best of luck - BTW, if you're about I think I'm going to head up to Tut's this week to collect my package, so will be able to take your's up at the same time if you haven't made alternate arrangements - there will be somebody here all day if you want to drop it off, you have my number.
Cheers,
Robin
