Thanks Dougal, should have thought about how to fit the PPs. Do you think the PPs would give a better result? Haven't fitted the electrolytics yet so for a small outlay would buy them if they're going to be better.
IMO, Polyprops would be the better upgrade- in the case of my TDLs, they brought a significant dollop more detail and overall balance to the sound, with treble 'breathiness' and imaging much improved from before. But then again the original electrolytics were probably just about shot...
PP or MFP (metallised film polypropylene) caps tend to have tighter tolerances than electrolytics, and will often result in the speakers sounding better than when they were new. Also, they don't degrade like electrolytics so once it's done, it's done.
I would think that any difference you may hear by installing new electrolytics will depend entirely on what state the current ones are in. Changing to polyprops would, in my opinion, be the way to go- that way you're replacing like-for-better rather than like-for-like. Even if your current caps are still good, you will still notice an improvement.
I'm doing my Mission 780s this week so will report back... cheap, easy job though- a whole ONE 15mFd cap per crossover, although Mission had decided to glue the caps down in a little recess with the print obscured- I've had to remove them just to get the values! Then it will be the turn of my RTL G20s... I think I need psychiatric help. :O