see if you can find the manual for the engine and the parts breakdown of it .... it will show you how it all goes together and where the orings are at
Disassembly and inspection.
That is the only way to determine if they are not good.
Once you're in there, it makes sense to just put in new orings.
Do yourself a favor and buy a couole sets of orings*,Associated "Green Slime", a new air filter or 5*, a few glow plugs* and some new fuel line.
All of these items are reasonably inexpensive and WILL use eventually.
Rubber parts are all items that I would just go ahead and replace. You're starting off with no "old, cracked, dried out" parts if you replace all with new.
Eliminate those easy issues as possible causes of problems.
You will likely foul a glow plug before this is running correctly, just buy a 5 pack.
Be positive your fuel is brand new, fresh out of a sealed bottle that YOU bought and opened.
Fresh fuel is important and another potential cause of "no start" condition. Eliminate that.
Also be sure that you have a GOOD, WORKING glow plug ignitor!
They are cheap and eliminates another "no start" cause.
An extra glow plug ignitor IS your friend in nitro r/c!