This does sound more like a sticky, gummed-up mechanism than an issue with normal operation. Old lubricant can prevent the shutter/mirror-cocking parts from moving fully, which would explain the weak misfire sound and eventual jam.

Based on the advice given, a fast-evaporating electronics/contact cleaner is the safer first choice for freeing sticky parts and dissolving old residue. Use as little as possible and avoid getting cleaner on shutter curtains, focusing screens, or other delicate parts.

WD-40 is generally not a good choice for internal camera mechanisms. Even if it can loosen stuck parts, it leaves residue and overspray can migrate where it should not, attracting more dirt and causing future problems. If lubrication is needed after cleaning, use only a proper camera/watch-grade lubricant in tiny amounts.

If you need diagrams or disassembly guidance, a dedicated camera repair manual/site for the SRT101 may help.