So it seems you've got 2 different kind of problems; a draining problem and a starting one.

- For the starting problem I would make sure the battery is in good condition and fully loaded.
- Then with a pair of extra hands and a multimeter I would measure the voltages.
- First between the minus pole of the battery to the big plus connection on the startermotor itself. Measure it in in rest and than in starting position to see any differences.
- Than measure from the minus on the startmotor and the follow all the grounding connection unill you're back at the minus of the battery.

Always keep the minus connection of the multimeter to the minus pole on the battery and measure the voltages with the other pin to the different connections. With this kind of measurement you can easily find the bad connection because that has got a big voltage difference to earth when starting. A bad earth connection will give a little to non voltage readout at rest (between the negative pole of the battery and the connection) and a higher value when starting the car at one point of the connection and no voltage readout at the other side of the connection.

Hope this will help you.