In his blog no. 397 of the 23rd of April Jack Windsor Lewis mentions some weakform words that either are not recorded in the established pron dictionaries or are marked as not belonging to RP. This blog entry of his is a welcome widening of the concept of weakforms extending the usual and fairly narrow list of such words. One of these 'cast-outs' is the adverb only. According to Windsor Lewis's observation "a very large majority of educated English speakers worldwide frequently use ell-less weakforms of only." The examples he gives are two short extracts from the 1964 Paramount film about (Thomas) Becket. The first example is a sentence spoken by Donald Wolfit (at about 1:25:05), who plays the role of Bishop Folliot: "My only interest is for the church."
The second one is a section with John Gielgud as King Louis VII saying (at about 1:45:52): "In the meantime, however, we can only express our astonishment. No news has reached us of the Archbishop of Canterbury's presence [...]."
credit: Paramount Pictures
BTW: These are not the only ell-less onlys in this film.