Ebay is a great resource but I do like Amazon more for a few reasons. Namely, if you are a PRIME member, you can get 2 day free shipping and most importantly I do like the return policy of Amazon.
The disc shaped ones will fit, you just have to be patient. I have even bent the pins a bit to make it easier to insert. They give off very little heat so if they are touching it make little difference. The bulb shaped LED's will rely more on the refelctor and I found them to not give off as good a light, where as the disc shaped threw the light "downward".
I typically, order a small batch of what I think would be a good replacement and then install them. I then let them run for at least 24hours to see if they will fail. You would be surprised at how many do. I have found
this supplier to have good product. They are well priced and are pretty close to what the halogens produce. The 3watt throw a few more lumens so I have used in ceiling pots along the main walk way and 1.5 in other areas I want softer light.
I am for the most part complete in changing my entire unit over to LED, including exterior lighting such as patio lighting, driving lights, signals and markers. I have been described as a little bit obsessed with lights by the family here lol