You may add as many film capacitors you like but these have absolutely nothing to do with offset.
You may replace as many of the main caps you like but these also have nothing to do with offset
You may actually remove totally the main capacitors ( for experiment ) and replace them with anything available from capacitance aspect as low as 100uf in the rated voltage still offset has nothing to do with it ....( static conditions )
A slight mismatching on the LTP and slight changes on the thermals ( like starting measuring with the top cover on or without ) are responsible for the small variations in the offset of that level and LTP is so sensitive that in most cases it is enough to blow your breath on it and there is going to be minor change in the offset ...
Still this behavior is expected to almost any amplifier and variations of that level are expected while these are by no means responsible to blown tweeters .
Ferrofluid does not evaporate though the chemical composition inside the driver might change if excessive temperature is produced , coil of the driver is getting toasted and leftovers of the coil is mixed with the ferrofluid ...( clearly not the case here )
Your tweeters blow from optimistic design of the xovers and the general aspect of the speaker to have a rich high mid area even though a tweeter found in the wrong power , wrong peak , wrong frequency every now and then might blow ...
Both offset and ferrofluid have nothing to do with ..Actually writing these things is between laughing or screaming
If you been reading this about film capacitors in the internet you have been probably reading the wrong fairy tale or the wrong urban legend ...
If the tech dude in the speaker shop was telling things like the above then YES you have been fooled around big time ...
If film capacitor story is your own knowledge or idea keep away from anything that has a cable on it ....for safety reasons ....