LPG is EXACTLY OPPOSITE OF LARGER!
LPG, IE propane is a much smaller molecule.
Among other problems I'll get to later..
If you have a leak with r134a, its going to be MUCH worse with propane
R-134a Tetrafluoroethane, molecular mass 102.03
R-290 Propane, molecular mass 44.097
Sourced here
https://www.engineeringtoolbox.com/refrigerants-d_902.html Also, your line pressures, head pressure, and head temperatures are going to be much higher.
The higher pressures alone can cause things to get worse since system was not designed for it,
Also when the compressor was not designed for it, or the system was not designed for it, the head temperatures will destroy the pump.
Now if that was not enough, since it was not designed for this, the evap to condenser ratio may cause other immediate troubles because of the boiling and liquid temperature points plus the difference in how much heat energy each can carry. The two refrigerants have a lot of differences.
Theoretically... (Now I cannot legally tell you to do this) there are propane-butane mixes.
Some sold as HC-12a that can normally work as a replacement as long as you find and fix the problem. It should be 100% compatible with any oil.
Though like I alluded to, many countries restrict this stuff/modification to the extreme!
However, HC-12a can work better, and be more efficient. Just it introduces a fire risk.
So, in this case, if it was designed for r134a, and you can still get it, replace it with the same.
Further interesting read.
https://www.vasa.org.au/wp-content/uploads/2012/10/Oct2012vasa_HCwhite_paper.pdf Most sealed systems like this won't have a UV tracer from the factory, so adding that may help find the problem.
Keep in mind if you add a tracer UV dye with oil, it takes up space the freon would have.
This will reduce cooling capacity slightly and reduce efficiency once you add more of anything not freon past the original design spec.
But, if it helps to repair the problem, so be it.
To draw down and recharge a system without having to solder you can buy a piercing valve
https://www.amazon.com/Supco-BPV31-Bullet-Piercing-Valve/dp/B00DM8J3MIIt's not the absolute best option of course but it tends to get the job done much easier.
Best of luck.