Eric...
It sounds like (to me) that your battery posts, connectors, or cables are corroding between starts... and likely in a few other places. The clip-clop you're hearing is the starter solenoid engaging... and note that it's not a 'starter'... it's a starter-generator (s-g)... not quite the same as a typical starter. It does have brushes, and you might have one brush or commutator pole that's bad... in which case, you could simply turn the motor just a tad, try the key, and get successful results. It doesn't sound like that's been the condition, but you may wanna give it a check just-in-case.
Try something... try starting it, with just the clip-clop... hold the key in the start position for about 5 seconds. Release the key. Feel the following posts and cables:
battery posts
Ground cable from SG to frame
Ground cable from battery to frame
posts on starter solenoid (under dash- lift hood, reach under fuel-tank)
All of these connections should be stone-cold. If they're warm, it's because there's resistance in the wire or connection.
Since you say cleaning/tightening the cables has a positive effect, it's reasonable to assume that you've determined the problem, but not localized it. If you find a warm cable or connection, you've localized it.
Two things that would make what you describe happen include:
--stray battery acid working between the posts and cable connectors.
--a cable that has wicked in moisture (by capillary action), and corroded somewhere INSIDE the length of the cable, probably not too far from the battery, and by disconnecting, cleaning, and reassembling the connectors, you're partially re-establishing the connection.
For the first, take a cup of water, and put a tablespoon of baking soda (sodium bicarbonate) on each post and clamp, sprinkle in some water, and scrub it with a toothbrush... rinse it again, get all the stuff of.
For the second, take the cables in your hands, one at a time, and flex 'em back and forth every inch or two. If you get to a point that feels 'crunchy', just take it off and replace it. If you take a knife and strip the insulation off, you'll find that the 'crunchy' area is full of green powder, and very little wire... the green crunchy stuff is oxidized copper, no longer capable of carrying current worth a darn.
FWIW, I've found battery cables 5' long, where a segment right in the middle was corroded to junk, but the ends looked perfect.
