As a late note to this problem relating to items stuck one in another. My ignorant mind always pondered what was going on in my old Jaguar engines which had an aluminum alloy cylinder sleeve pressed into the steel engine block when starting the car at a temperature around 30°F and which then quickly would reach approx. 200°F or more. It just kind of scared me thinking about it.
Anyways, dealing with removing and/or installing bearings, sleeves, tubes, shafts, etc. over the years I have, as the last couple previous posts mentioned, used temperature differential as a primary method to obtain the desired results whether on brand new parts or old rusted/corroded parts. Especially on old parts "welded" via galvanic action or oxidation that did not readily come apart with reasonable normal effort before applying any excessive force (e.g. hammering, leveraged twisting, etc.) that could possibly damage one or both parts in question; and before adding any solutions that might also cause damage to parts, but also damage finishes (paint, plating, decals, etc.). I would also include the use of excessive heat that could cause any damage to finishes (especially paint, decals) or possibly change the temper of the part(s) involved (should not be an issue with cooling; unless using liquid nitrogen!).
The nice thing is that most of us already have, or can easily obtain a means of heating and cooling the project in question at a fairly low cost.
Even though steel on steel, and aluminum on aluminum expansion/contraction is going to be minimal between parts (unless of identical alloy composition; and even then the molecular "grain" still has an effect), heating and cooling will still help to weaken a corrosive bond. It can also allow certain chemical products to function better due to increased penetration (spacial differential/capillary action). With aluminum on steel, given aluminum has a substantially greater (in relative terms) amount of expansion/contraction than steel, it stands to reason that a corrosive bond will be disrupted much more than steel on steel/aluminum on aluminum, and I really don't worry about heating very much with an aluminum part in a steel tube (seat post or stem) because it will only make it a tighter fit (though it possibly affects the bond integrity slightly). Even at an ambient starting temperature (unless you working in the cold already), if you cool the parts to freezing or below you should have reduced the size of the aluminum part more than the steel part, and allow better penetrating of your pretreatment (zip lock bag or plastic wrap parts to prevent water intrusion unless you desire it). Keep it as cool as possible by working quickly before it warms back up and then try different removal methods. Cooling and allowing to rewarm multiple times is preferrable before applying physical means to separate parts.
Heating: In many cases a hair dryer on high provides sufficient heat without any ill effects; next an oven (at lower or higher temps if you can fit parts in it) or a heat gun at low or high; lastly the torch (I have at times used a micro torch as a means to focus heat in a smaller area).
Cooling: bucket/tub/pool of ice water or freezer it parts will fit in it; next dry ice (a CO2 fire extinguisher can work for this also).
Warning always wear proper safety gear for high and low temp., and chemical methods. Remember some cjemicals readily ignite with open flame and high heat!
Pretreatments: I have used WD40, PB Blaster (better), and Kroil (best, at least for steel/iron). No experience with LPS-1.
I have used these methods for commercial and personal work. I have yet to damage any parts or frames over the past 30 years. I have damaged paint, but not on a project where that was a concern be it for a client's project (get permission first!) or my own.
