The Spectator 1902

[Matakari]

I am stuck. Some help on the following, please!
ACROSS
12. Youth imbued with right stuff ( 4 ) : ??L?
13. Massage wet back around base (5 ) :???A?
15. Material in varied festival ( 10 ): ?E??I??W??
23. Second leader of this island ( 4 ): ??T
31. Porcelain, for example, man in middle of burglary left ( 8 ): E???????
DOWN:
18. Compact tin? Good ( 4 ): ?N??
19. Solid ground reached? Teacher accepts that ( 10 )
?E????????
Many thanks for your patience!

[shaneystar2]

12 La(r)d
13 Knead...
15 Terminalia ..anag material in
23 Motu
31 Eggshell
18 (SN)ug
19 Decahedron

[JMR27]

31 e.g. g she ll (but don't know where the s comes from)
18. sn u g (but don't know where the u comes from)

are there special instructions with this crossword?

[bathtub]

Yes. The preamble indicates that in 7 clues, the wordplay omits reference to one letter of the answer.

[Matakari]

Thanks a lot for the help!