Some games, like Pop'n SD cabinets, were designed with traditional filament bulbs in mind. They have a warm up threshold voltage that barely doesn't light up the bulb so they don't burn out quickly from turning off and on a lot. If you want to use LEDs on these cabinets you need bulbs that defeat the warmup voltage, which are called "non ghosting" bulbs. These are commonly sold on pinball restoration sites like comet pinball, however they are usually sold in 6.3V packages so you may have to take apart the bulb and beef up the power supply resistors to dissipate the excess voltage.

If you would like to color match your LEDs to your old filament bulbs you should purchase "Warm White" LEDs.

Chinese manufacturers have started putting a lip on a lot of 12v cob bulbs which make them catch on the top spring holder so they will just barely not fit into a sanwa pushbutton. To fix this you can either grind down the excess plastic with a dremel or replace the casing with a case that fits. To do this, take the led out of its casing by straightening the contact leads and pulling on the top. Good wedge donors that do fit are dead Sanwa bulbs, Comet Pinball 6.3V Twin 2835s, and ISTMALL LEDs. Superbright LEDs work as well but notoriously don't fit in lamp holders very well and often need to be readjusted as they will pop out. Sanwa LEDs have a tiny amount of adhesive so pry on the edge of the cob with a knife.