Take it to a gunsmith. You did not say what is wrong with it.
100-300 USD
Moondog Industries gas fill O-rings from evike.com. Quick, easy, and inexpensive.
the serial number on your ruger P345 is located on the right side of the firearm directly beneath the slide. its a silver looking plate with an 8 digit number.
100-400 USD or so
100-400 USD or so depending on specifics
if you mean the air soft pistol then yes it can take both 0.12 and 0.43 plastic bb's
Magazine
The Ruger SR9 uses a proprietary magazine.
MidWay
neither, also it doesn't matter which one is "stronger", if you have a a high FPS (strong), you can't play on fields
You need the help of a gunsmith
No, a Pro Mag Ruger LCP magazine will not fit in a Lorcin .380. The Ruger LCP and Lorcin .380 are different firearms with distinct magazine designs and dimensions. While both are .380 caliber, their magazine compatibility does not overlap due to differences in their construction and specifications. Always use the manufacturer's recommended magazines for safety and reliability.