Last two. 28a Skin shows signs of ageing, we hear g?a??
21d Thought of Rosa Klebb in action d?e???. [Rosa Klebb is the setter]
Last letter of 28a is fifth letter of 21d
In addition I can't parse
2d Revolutionary new doctor dropping Oscar in it. Insurgent (=Revolutionary)
16a Spooner's misfortunes necessitate a bloody complaint. Nosebleed
17d Hispanic misses most mockery I've picked up. Senoritas.(=unmarried Spanish lady)
Thanks