First about sights, I use a Red Dot on my TM-15s and the only way to do that is to use a TM Series RipClip. I use RipClips and have not had any issues. Mil Sim markers are not as easy for me to aim without a red dot, so for me they are a requirement.
As for the Spring, there is a small end and larger end on their springs. You want to make sure the spring "clicks" onto the bolt when you put it on. It will then also "click" into a notch on the inside of the main body when you reinsert the bolt and bolt guide. This will result in the spring and sometimes the bolt as well staying behind in the marker when it is removed. I will use a swab to push the spring out from the front of the marker when necessary.
You should post a pic of your new family member! The TM-15 is my favorite Mil Sim marker that I currently own.
Unofficial Pack Elephant of the CFLL. Up to 22 Pods + up to 900 rounds on the Hammer carried on to the field. 32 Pods with Optional dump bag.
Current Darkside Markers
FIN Camo Luxe 2.0/ Faded Splash Luxe 2.0/ Tactical Warlord Vcom/ Digital Camo Ripper Victory/ Dark Stripper Geo3/ Multicam Ego11/ Bob Long MVP/ Zodiac ZR-1