Checking a used solar panel

Hi all

I have the chance to buy a "few" year old BP solar panel (model 275 which I assume is 75W nominal) for a good price of $450. However before I buy it, I wanted to check it was still in good condition. I measured the output voltage at the terminal block (has 2 bypass diodes) and it measured 21.3V and at the end of ~10m of heavy cable (~6mm sq area) it was 21.1V. That is (I assume) the short circuit voltage and seems about right. I also measured the current at the end of the long lead and it was 3.7A. Did not think to do the same at the terminal block. This seemed a bit low as the spec sheet says 4.75A short circuit. Is there something wrong with the panel and should I run far away? Or is the drop because of the diodes, the lack of ability of the tester (me) or something else? The panel appear to be in ok condition, a little bit of corrosion on the braid that comes out of the back of the panel (I think it was used on a boat).

Also, when connected through a regulator, which I assume steps the voltage down, does the current increase?

Thanks for any help
Tim